As filed with the Securities and Exchange Commission on October 3, 2013

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF
1933

Twitter, Inc.

(Exact name
of Registrant as specified in its charter)

Delaware

7370

20-8913779

(State or other jurisdiction of incorporation or organization)

(Primary Standard Industrial

Classification Code Number)

(I.R.S. Employer

Identification Number)

1355 Market Street, Suite 900

San Francisco, California 94103

(415) 222-9670

(Address, including zip code, and telephone number, including area code, of Registrants principal executive
offices)

Richard Costolo

Chief
Executive Officer

Twitter, Inc.

1355 Market Street, Suite 900

San Francisco, California 94103

(415) 222-9670

(Name,
address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Steven E. Bochner, Esq.

Katharine A. Martin, Esq.

Rezwan D. Pavri, Esq.

Wilson Sonsini Goodrich & Rosati, P.C.

650 Page Mill Road

Palo Alto, California 94304

(650) 493-9300

Vijaya Gadde, Esq.

Sean Edgett, Esq.

Twitter, Inc.

1355 Market Street, Suite 900

San Francisco, California 94103

(415) 222-9670

Alan F. Denenberg, Esq.

Davis Polk & Wardwell LLP

1600 El Camino Real

Menlo Park, California 94025

(650) 752-2000

Approximate date of commencement of proposed sale to the public: As soon as practicable after this registration statement becomes effective.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the
Securities Act, check the following box: ¨

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following
box and list the Securities Act registration statement number of the earlier effective registration statement for the same
offering. ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective
registration statement for the same offering. ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities
Act registration statement number of the earlier effective registration statement for the same offering. ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated
filer, a non-accelerated filer, or a smaller reporting company. See the definitions of large accelerated filer, accelerated filer and smaller reporting company in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer

¨

Accelerated filer

¨

Non-accelerated filer

x (Do not check if a
smaller reporting company)

Smaller reporting company

¨

CALCULATION OF REGISTRATION FEE

Title of Each Class of Securities to be Registered

Proposed MaximumAggregateOffering
Price(1)(2)

Amount ofRegistration Fee

Common Stock, $0.000005 par value per share

$1,000,000,000

$128,800

(1)

Estimated solely for the purpose of computing the amount of the registration fee pursuant to Rule 457(o) under the Securities Act of 1933, as amended.

(2)

Includes the aggregate offering price of additional shares that the underwriters have the right to purchase from the Registrant, if any.

The Registrant hereby amends this registration statement on such date or dates as may be necessary to delay its
effective date until the Registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the
registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. These securities
may not be sold until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell nor does it seek an offer to buy these securities in any jurisdiction where the
offer or sale is not permitted.

Subject To
Completion. Dated October 3, 2013.

Shares

Twitter, Inc.

Common Stock

This is an initial public
offering of shares of common stock of Twitter, Inc.

Prior to this offering, there has been no public market for the common stock. It is
currently estimated that the initial public offering price per share will be between $ and $ . We intend to list the common stock on the
under the symbol TWTR.

We are an emerging
growth company as defined under the federal securities laws and, as such, may elect to comply with certain reduced public company reporting requirements for future filings.

See Risk Factors beginning on page 16 to read about factors you should consider before buying shares of
the common stock.

Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved of these securities or passed upon the
accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

Per Share

Total

Initial public offering price

$

$

Underwriting discount

$

$

Proceeds, before expenses, to Twitter

$

$

To the extent that the underwriters sell more than
shares of common stock, the underwriters have the option to purchase up to an additional shares from
Twitter at the initial public offering price less the underwriting discount.

The underwriters expect
to deliver the shares against payment in New York, New York on , 2013.

Through and including ,
2013 (the 25th day after the date of this prospectus), all dealers effecting transactions in these securities, whether or not participating in this offering, may be required to deliver a prospectus. This is in addition to a dealers obligation
to deliver a prospectus when acting as an underwriter and with respect to an unsold allotment or subscription.

We have not authorized
anyone to provide any information or to make any representations other than those contained in this prospectus or in any free writing prospectuses we have prepared. We take no responsibility for, and can provide no assurance as to the reliability
of, any other information that others may give you. This prospectus is an offer to sell only the shares offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so. The information contained in this prospectus is
current only as of its date.

This summary highlights selected information that is presented in greater detail elsewhere in this prospectus. This summary does not contain all
of the information you should consider before investing in our common stock. You should read this entire prospectus carefully, including the sections titled Risk Factors and Managements Discussion and Analysis of Financial
Condition and Results of Operations and our consolidated financial statements and the related notes included elsewhere in this prospectus, before making an investment decision. Unless the context otherwise requires, the terms
Twitter, the company, we, us and our in this prospectus refer to Twitter, Inc. and its consolidated subsidiaries.

TWITTER, INC.

Twitter is a
global platform for public self-expression and conversation in real time. By developing a fundamentally new way for people to create, distribute and discover content, we have democratized content creation and distribution, enabling any voice to echo
around the world instantly and unfiltered.

Our platform is unique in its simplicity: Tweets are limited to 140 characters of text. This
constraint makes it easy for anyone to quickly create, distribute and discover content that is consistent across our platform and optimized for mobile devices. As a result, Tweets drive a high velocity of information exchange that makes Twitter
uniquely live. We aim to become an indispensable daily companion to live human experiences.

People are at the heart of
Twitter. We have already achieved significant global scale, and we continue to grow. We have more than 215 million monthly active users, or MAUs, and more than 100 million daily active users, spanning nearly every country. Our users
include millions of people from around the world, as well as influential individuals and organizations, such as world leaders, government officials, celebrities, athletes, journalists, sports teams, media outlets and brands. Our users create
approximately 500 million Tweets every day.

Twitter is a public, real-time platform where any user can create a Tweet and any user
can follow other users. We do not impose restrictions on whom a user can follow, which greatly enhances the breadth and depth of available content and allows users to discover the content they care about most. Additionally, users can be followed by
thousands or millions of other users without requiring a reciprocal relationship, enhancing the ability of our users to reach a broad audience. The public nature of our platform allows us and others to extend the reach of Twitter content beyond our
properties. Media outlets distribute Tweets beyond our properties to complement their content by making it more timely, relevant and comprehensive. Tweets have appeared on over one million third-party websites, and in the second quarter of 2013
there were approximately 30 billion online impressions of Tweets off of our properties.

Twitter provides a compelling and efficient way
for people to stay informed about their interests, discover what is happening in their world right now and interact directly with each other. We enable the timely creation and distribution of ideas and information among people and organizations at a
local and global scale. Our platform allows users to browse through Tweets quickly and explore content more deeply through links, photos, media and other applications that can be attached to each Tweet. As a result, when events happen in the world,
whether planned, like sporting events and television shows, or unplanned, like natural disasters and political revolutions, the digital experience of those events happens in real time on Twitter. People can communicate with each other during these
events as they occur, creating powerful shared experiences.

We are inspired by how Twitter has been used around the world. President Obama used our platform
to first declare victory publicly in the 2012 U.S. presidential election, with a Tweet that was viewed approximately 25 million times on our platform and widely distributed offline in print and broadcast media. A local resident in Abbottabad,
Pakistan unknowingly reported the raid on Osama Bin Ladens compound on Twitter hours before traditional media and news outlets began to report on the event. During the earthquake and subsequent tsunami in Japan, people came to Twitter to
understand the extent of the disaster, find loved ones and follow the nuclear crisis that ensued. For individuals and organizations seeking timely distribution of content, Twitter moves beyond traditional broadcast mediums by assembling connected
audiences. Twitter brings people together in shared experiences allowing them to discover and consume content and just as easily add their own voice in the moment.

Our platform partners and advertisers enhance the value we create for our users.

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Platform Partners. Millions of platform partners, which include publishers, media outlets and developers, have integrated with
Twitter, adding value to our user experience by contributing content to our platform, broadly distributing content from our platform across their properties and using Twitter content and tools to enhance their websites and applications. Many of the
worlds most trusted media outlets, including the BBC, CNN and Times of India, regularly use Twitter as a platform for content distribution.

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Advertisers. Advertisers use our Promoted Products, the majority of which are pay-for-performance, to promote their brands,
products and services, amplify their visibility and reach, and complement and extend the conversation around their advertising campaigns. We enable our advertisers to target an audience based on a variety of factors, including a users Interest
Graph. The Interest Graph maps, among other things, interests based on users followed and actions taken on our platform, such as Tweets created and engagement with Tweets. We believe a users Interest Graph produces a clear and real-time signal
of a users interests, greatly enhancing the relevance of the ads we can display for users and enhancing our targeting capabilities for advertisers.

Although we do not generate revenue directly from users or platform partners, we benefit from network effects where more activity on Twitter results in the creation and distribution of more content, which attracts
more users, platform partners and advertisers, resulting in a virtuous cycle of value creation.

Mobile has become the primary driver of
our business. Our mobile products are critical to the value we create for our users, and they enable our users to create, distribute and discover content in the moment and on-the-go. The 140 character constraint of a Tweet emanates from our origins
as an SMS-based messaging system, and we leverage this simplicity to develop products that seamlessly bridge our user experience across all devices. In the three months ended June 30, 2013, 75% of our average MAUs accessed Twitter from a mobile
device, including mobile phones and tablets, and over 65% of our advertising revenue was generated from mobile devices. We expect that the proportion of active users on, and advertising revenue generated from, mobile devices, will continue to grow
in the near term.

We have experienced rapid growth in our revenue in recent periods. From 2011 to 2012, revenue increased by 198% to
$316.9 million, net loss decreased by 38% to $79.4 million and Adjusted EBITDA increased by 149% to $21.2 million. From the six months ended June 30, 2012 to the six months ended June 30, 2013, revenue increased by 107% to $253.6 million, net
loss increased by 41% to $69.3 million and Adjusted EBITDA increased by $20.7 million to $21.4 million. For information on how we define and calculate Adjusted EBITDA, and a reconciliation of net loss to Adjusted EBITDA, see the
section titled Summary Consolidated Financial and Other DataNon-GAAP Financial Measures.

We have also experienced significant growth in our user base, as measured by MAUs, and user
engagement, as measured by timeline views.

For information on how we define and calculate the number of MAUs and the number of timeline views and factors that can affect
these metrics, see the sections titled Managements Discussion and Analysis of Financial Condition and Results of OperationsKey Metrics and Industry Data and Company Metrics.

The Evolution of Content Creation, Distribution and Discovery

The Internet and digitization have allowed for virtually all content to be made available online, but the vast array of content has made it difficult for people to find what is important or relevant to them. Over
time, technologies have been developed to address this challenge:

Web Browsers. In the early to
mid-1990s, browsers, including Netscape Navigator and Internet Explorer, presented content on the Internet in a visually appealing manner and allowed people to navigate to specific websites, but the content experience was generally not personalized
or tailored to a persons interests and information was often difficult to find.

Web Portals. In the
mid to late-1990s, Yahoo!, AOL, MSN and other web portals aggregated and categorized popular content and other communication features to help people discover relevant information on the Internet. These portals, while convenient, and with some
ability to personalize, offer access to a limited amount of content.

Search Engines. In the early-2000s,
Google and other search engines began providing a way to search a vast amount of content, but search results are limited by the quality of the search algorithm and the amount of content in the search index. In addition, given the lag between live
events and the creation and indexing of digital content, search engine results may lack real-time information. Also, search engines generally do not surface content that a person has not requested, but may find interesting.

Social Networks. In the mid-2000s, social networks, such as Facebook, emerged as a new way to connect with friends
and family online, but they are generally closed, private networks that do not include content from outside a persons friends, family and mutual connections. Consequently, the depth and breadth of content available to people is generally
limited. Additionally, content from most social networks is not broadly available off their networks, such as on other websites, applications or traditional media outlets like television, radio and print.

Twitter continues the evolution of content creation, distribution and discovery by combining the following four elements at scale to create a global platform for public self-expression and conversation in real
time. We believe Twitter can be the content creation, distribution and discovery platform for the Internet and evolving mobile ecosystem.

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Public. Twitter is open to the world. Content on Twitter is broadly accessible to our users and unregistered visitors. All users
can create Tweets and follow other users. In addition, because the public nature of Twitter allows content to travel virally on and off our properties to other websites and media, such as television and print, people can benefit from Twitter content
even if they are not Twitter users or following the user that originally tweeted.

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Real-Time. News breaks on Twitter. The combination of our tools, technology and format enables our users to quickly create and
distribute content globally in real time with 140 keystrokes or the flash of a photo, and the click of a button. The ease with which our users can create content combined with our broad reach results in users often receiving content faster than
other forms of media.

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Conversational. Twitter is where users come to express themselves and interact with the world. Our users can interact on Twitter
directly with other users, including people from around the world, as well as influential individuals and organizations. Importantly, these interactions can occur in public view, thereby creating an opportunity for all users to follow and
participate in conversations on Twitter.

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Distributed. Tweets go everywhere. The simple format of a Tweet, the public nature of content on Twitter and the ease of
distribution off our properties allow media outlets to display Tweets on their online and offline properties, thereby extending the reach of Tweets beyond our properties. A 2013 study conducted by Arbitron Inc. and Edison Research found that 44% of
Americans hear about Tweets through media channels other than Twitter almost every day.

Our Value Proposition to Users

People are at the heart of Twitter. We have more than 215 million MAUs from around the world. People come to Twitter for many
reasons, and we believe that two of the most significant are the breadth of Twitter content and our broad reach. Our users consume content and engage in conversations that interest them by discovering and following the people and organizations they
find most compelling.

Our platform provides our users with the following benefits:

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Sharing Content with the World. Users leverage our platform to express themselves publicly to the world, share with their friends
and family and participate in conversations. The public, real-time nature and tremendous global reach of our platform make it the content distribution platform of choice for many of the worlds most influential individuals and organizations, as
well as millions of people and small businesses.

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Discovering Unique and Relevant Content. Twitters over 215 million MAUs, spanning nearly every country, provide great
breadth and depth of content across a broad range of topics, including literature, politics, finance, music, movies, comedy, sports and news.

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Breaking News and Engaging in Live Events. Users come to Twitter to discover what is happening in the world right now directly from
other Twitter users. On Twitter, users tweet about live events instantly, whether it is celebrities tweeting to their fans, journalists breaking news or people providing eyewitness accounts of events as they unfold. Many individuals and

organizations choose to break news first on Twitter because of the unique reach and speed of distribution on our platform. As a result, Twitter is a primary source of information and complements
traditional media as a second screen, enhancing the overall experience of an event by allowing users to share the experience with other users in real time. We believe this makes Twitter the social soundtrack to life in the moment.

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Participating in Conversations. Through Twitter, users not only communicate with friends and family, but they also participate in
conversations with other people from around the world, in ways that would not otherwise be possible. In addition to participating in conversations, users can simply follow conversations on Twitter or express interest in the conversation by
retweeting or favoriting.

Our Value Proposition to Platform Partners

The value we create for our users is enhanced by our platform partners, which include publishers, media outlets and developers. These platform
partners have integrated with Twitter through an application programming interface, or API, that we provide which allows them to contribute their content to our platform, distribute Twitter content across their properties and use Twitter content and
tools to enhance their websites and applications. We provide a set of development tools, APIs and embeddable widgets that allow our partners to seamlessly integrate with our platform.

We provide our platform partners with the following benefits:

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Distribution Channel. Platform partners use Twitter as a complementary distribution channel to expand their reach and engage with
their audiences. Publishers and media outlets contribute content created for other media channels to Twitter and tweet content specifically created for Twitter. We provide platform partners with a set of widgets that they can embed on their websites
and an API for their mobile applications to enable Twitter users to tweet content directly from those properties. As our users engage with this content on Twitter, they can be directed back to our partners websites and applications.

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Complementary Real-Time and Relevant Content. Twitter enables platform partners to embed or display relevant Tweets on their online
and offline properties to enhance the experience for their users. Additionally, by enhancing the activity related to their programming or event on Twitter, media outlets can drive tune-in and awareness of their original content, leveraging
Twitters strength as a second screen for television programming. For example, during Super Bowl XLVII, over 24 million Tweets regarding the Super Bowl were sent during the game alone and 45% of television ads shown during the Super Bowl
used a hashtag to invite viewers to engage in conversation about those television ads on Twitter.

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Canvas for Enhanced Contentwith Twitter Cards. Platform partners use Twitter Cards to embed
images, video and interactive content directly into a Tweet. Twitter Cards allow platform partners to create richer content that all users can interact with and distribute.

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Building with Twitter Content. Platform partners leverage Tweets to enhance the experience for their users. Developers incorporate
Twitter content and use Twitter tools to build a broad range of applications. Media partners incorporate Twitter content to enrich their programming and increase viewer engagement by providing real-time Tweets that express public opinion and
incorporate results from viewer polls on Twitter.

We provide compelling value to our advertisers by delivering the ability to reach a large global audience through our unique set of advertising
services, the ability to target ads based on our deep understanding of our users and the opportunity to generate significant earned media. Advertisers can use Twitter to communicate directly with their followers for free, but many choose to purchase
our advertising services to reach a broader audience and further promote their brands, products and services.

Our platform provides our
advertisers with the following benefits:

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Unique Ad Formats Native to the User Experience. Our Promoted Products, which are Promoted Tweets, Promoted Accounts and Promoted
Trends, provide advertisers with an opportunity to reach our users without disrupting or detracting from the user experience on our platform.

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Targeting. Our pay-for-performance Promoted Products enable advertisers to reach users based on many factors. Importantly, because
our asymmetric follow model does not require mutual follower relationships, people can follow the users that they find most interesting. These follow relationships are then combined with other factors, such as the actions that users take on our
platform, including the Tweets they engage with and what they tweet about, to form a users Interest Graph. We believe a users Interest Graph produces a clear and real-time signal of a users interests, greatly enhancing our
targeting capability.

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Earned Media and Viral Global Reach. The public and widely distributed nature of our platform enables Tweets to spread virally,
potentially reaching all of our users and people around the world. Our users retweet, reply to or start conversations about interesting Tweets, whether those Tweets are Promoted Tweets or organic Tweets by advertisers. An advertiser only gets
charged when a user engages with a Promoted Tweet that was placed in a users timeline because of its promotion. By creating highly compelling and engaging ads, our advertisers can benefit from users retweeting their content across our platform
at no incremental cost.

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Advertising in the Moment. Twitters real-time nature allows our advertisers to capitalize on live events, existing
conversations and trending topics. By using our Promoted Products, advertisers can create a relevant ad in real time that is shaped by these events, conversations and topics.

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Pay-for-Performance and Attractive Return on Investment. Our advertisers pay for Promoted Tweets and Promoted Accounts on a
pay-for-performance basis. Our advertisers only pay us when a user engages with their ad, such as when a user clicks on a link in a Promoted Tweet, expands a Promoted Tweet, replies to or favorites a Promoted Tweet, retweets a Promoted Tweet for the
first time, follows a Promoted Account or follows the account that tweets a Promoted Tweet. The pay-for-performance structure aligns our interests in delivering relevant and engaging ads to our users with those of our advertisers.

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Extension of Offline Advertising Campaigns. Twitter advertising complements offline advertising campaigns, such as television ads.
Integrating hashtags allows advertisers to extend the reach of an offline ad by driving significant earned media and continued conversation on Twitter.

Our Value Proposition to Data Partners

We offer data licenses that allow our data partners to
access, search and analyze historical and real-time data on our platform. Since the first Tweet, our users have created over 300 billion Tweets

spanning nearly every country. Our data partners use this data to generate and monetize data analytics, from which data partners can identify user sentiment, influence and other trends. For
example, one of our data partners applies its algorithms to Twitter data to create and sell products to its customers that identify activity trends across Twitter which may be relevant to its customers investment portfolios.

Growth Strategy

We have aligned our growth
strategy around the three primary constituents of our platform: users, platform partners and advertisers.

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Users. We believe that there is a significant opportunity to expand our user base. Industry sources estimate that as of 2012 there
were 2.4 billion Internet users and 1.2 billion smartphone users, of which only 215 million are MAUs of Twitter.

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Geographic Expansion. We plan to develop a broad set of partnerships globally to increase relevant local content on our platform
and make Twitter more accessible in new and emerging markets.

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Mobile Applications. We plan to continue to develop and improve our mobile applications to drive user adoption of these
applications.

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Product Development. We plan to continue to build and acquire new technologies to develop and improve our products and services and
make our platform more valuable and accessible to people around the world. We also plan to continue to focus on making Twitter simple and easy to use, particularly for new users.

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Platform Partners. We believe growth in our platform partners is complementary to our user growth strategy and the overall
expansion of our platform.

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Expand the Twitter Platform to Integrate More Content. We plan to continue to build and acquire new technologies to enable our
platform partners to distribute content of all forms.

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Partner with Traditional Media. We plan to continue to leverage our media relationships to drive more content distribution on our
platform and create more value for our users and advertisers.

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Advertisers. We believe we can increase the value of our platform for our advertisers by enhancing our advertising services and
making our platform more accessible.

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Targeting. We plan to continue to improve the targeting capabilities of our advertising services.

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Opening our Platform to Additional Advertisers. We believe that advertisers outside of the United States represent a substantial
opportunity and we plan to invest to increase our advertising revenue from international advertisers, including by launching our self-serve advertising platform in selected international markets.

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New Advertising Formats. We intend to develop new and unique ad formats for our advertisers. For example, we recently introduced
our lead generation and application download Twitter Cards and Twitter Amplify, which allows advertisers to embed ads into real-time video content.

Our business is subject to numerous risks and uncertainties, including those highlighted in the section titled Risk Factors immediately
following this prospectus summary. These risks include, but are not limited to, the following:

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If we fail to grow our user base, or if user engagement or the number of paid engagements with our pay-for-performance Promoted Products, which we refer to as ad
engagements, on our platform decline, our revenue, business and operating results may be harmed;

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If our users do not continue to contribute content or their contributions are not valuable to other users, we may experience a decline in the number of users
accessing our products and services, which could result in the loss of advertisers and revenue;

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We generate the substantial majority of our revenue from advertising, and the loss of advertising revenue could harm our business;

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If we are unable to compete effectively for users and advertiser spend, our business and operating results could be harmed;

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Our operating results may fluctuate from quarter to quarter, which makes them difficult to predict;

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User growth and engagement depend upon effective interoperation with operating systems, networks, devices, web browsers and standards that we do not control;

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If we fail to expand effectively in international markets, our revenue and our business will be harmed;

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We anticipate that we will expend substantial funds in connection with the tax liabilities that arise upon the initial settlement of restricted stock units, or
RSUs, in connection with this offering, and the manner in which we fund that expenditure may have an adverse effect on our financial condition; and

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Existing executive officers, directors and holders of 5% or more of our common stock will collectively beneficially own % of our common
stock and continue to have substantial control over us after this offering, which will limit your ability to influence the outcome of important transactions, including a change in control.

Channels for Disclosure of Information

Investors, the media and others should note that, following the completion of this offering, we intend to announce material information to the
public through filings with the Securities and Exchange Commission, or the SEC, our corporate blog at blog.twitter.com, the investor relations page on our website, press releases, public conference calls and webcasts. We also intend to announce
information regarding us and our business, operating results, financial condition and other matters through Tweets on the following Twitter accounts: ,
and .

The information that is tweeted by the foregoing Twitter accounts could be deemed to be material information. As such, we encourage investors, the media and others to follow the Twitter accounts listed above and to
review the information tweeted by such accounts.

Any updates to the list of Twitter accounts through which we will announce information
will be posted on the investor relations page on our website.

Twitter, Inc. was incorporated in Delaware in April 2007. Our principal executive offices are located at 1355 Market Street, Suite 900, San Francisco, California 94103, and our telephone number is (415) 222-9670. Our website address is www.twitter.com. Information contained on, or that can be accessed through, our website does not constitute part of this prospectus and inclusions of our website address
in this prospectus are inactive textual references only.

Twitter, the Twitter bird logo, Tweet,
Retweet and our other registered or common law trademarks, service marks or trade names appearing in this prospectus are the property of Twitter, Inc. Other trademarks and trade names referred to in this prospectus are the property of
their respective owners.

We estimate that the net proceeds from the sale of shares of our common stock in this offering will be approximately
$ (or approximately $ if the underwriters option to purchase additional shares of our common stock from us is exercised in full), based upon the
assumed initial public offering price of $ per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, and after deducting estimated
underwriting discounts and commissions and estimated offering expenses payable by us.

The principal purposes of this offering are to increase our capitalization and financial flexibility, create a public market for our common stock and enable access
to the public equity markets for us and our stockholders. We intend to use the net proceeds from this offering for general corporate purposes, including working capital, operating expenses and capital expenditures. We also may use a portion of the
net proceeds to satisfy our anticipated tax withholding and remittance obligations related to the settlement of our outstanding RSUs. Additionally, we may use a portion of the net proceeds to acquire businesses, products, services or technologies.
However, except for our proposed acquisition of MoPub, Inc., or MoPub, in exchange for shares of our common stock, we do not have agreements or commitments for any material acquisitions at this time. See the section titled Use of
Proceeds for additional information.

Concentration of Ownership

Upon completion of this offering, our executive officers, directors and holders of 5% or more of our common stock will beneficially own, in the aggregate, approximately
% of our outstanding shares of common stock.

The number of shares of our common stock that will be outstanding after this offering is based on
472,613,753 shares of our common stock (including preferred stock on an as-converted basis) outstanding as of June 30, 2013, and excludes:

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44,157,061 shares of our common stock issuable upon the exercise of options to purchase shares of our common stock outstanding as of June 30, 2013, with a
weighted-average exercise price of $1.82 per share;

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59,913,992 shares of our common stock subject to RSUs outstanding as of June 30, 2013;

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116,512 shares of our common stock, on an as-converted basis, issuable upon the exercise of a warrant to purchase convertible preferred stock outstanding as of
June 30, 2013, with an exercise price of $0.34 per share;

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27,002,040 shares of our common stock subject to RSUs granted after June 30, 2013;

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up to 14,791,464 shares of our common stock issuable upon completion of our acquisition of MoPub; and

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shares of our common stock reserved for future issuance under our equity compensation
plans which will become effective prior to the completion of this offering, consisting of:

7,814,902 shares of our common stock reserved for future issuance under our 2007 Equity Incentive Plan, or our 2007 Plan (after giving effect to an increase of
20,000,000 shares of our common stock reserved for issuance under our 2007 Plan after June 30, 2013 and the grant of 27,002,040 shares of our common stock subject to RSUs granted after June 30, 2013), which number of shares will be added to the
shares of our common stock to be reserved under our 2013 Plan upon its effectiveness; and

Our 2013 Plan and ESPP each provide for annual automatic increases in the number of
shares reserved thereunder and our 2013 Plan also provides for increases to the number of shares that may be granted thereunder based on shares under our 2007 Plan that expire, are forfeited or otherwise repurchased by us, as more fully described in
the section titled Executive CompensationEmployee Benefit and Stock Plans.

Except as otherwise indicated, all
information in this prospectus assumes:



the automatic conversion of all outstanding shares of our Class A junior preferred stock and our convertible preferred stock into an aggregate of
333,099,000 shares of our common stock, the conversion of which will occur immediately prior to the completion of this offering;



the filing and effectiveness of our amended and restated certificate of incorporation in Delaware and the adoption of our amended and restated bylaws, each of
which will occur immediately prior to the completion of this offering; and



no exercise by the underwriters of their option to purchase up to an additional shares of
our common stock from us.

The following tables summarize our consolidated financial and other data. We have derived the summary consolidated statement of operations data for
the years ended December 31, 2010, 2011 and 2012 from our audited consolidated financial statements included elsewhere in this prospectus. We have derived the summary consolidated statement of operations data for the six months ended June 30,
2012 and 2013 and our balance sheet data as of June 30, 2013 from our unaudited interim consolidated financial statements included elsewhere in this prospectus. The unaudited interim consolidated financial statements have been prepared on the same
basis as the audited consolidated financial statements and reflect, in the opinion of management, all adjustments of a normal, recurring nature that are necessary for a fair statement of the unaudited interim consolidated financial statements. Our
historical results are not necessarily indicative of the results that may be expected in the future and the results in the six months ended June 30, 2013 are not necessarily indicative of results to be expected for the full year or any other period.
The following summary consolidated financial and other data should be read in conjunction with the section titled Managements Discussion and Analysis of Financial Condition and Results of Operations and our consolidated financial
statements and related notes included elsewhere in this prospectus.

Year Ended December 31,

Six Months EndedJune 30,

2010

2011

2012

2012

2013

(In thousands, except per share data)

Consolidated Statement of Operations Data:

Revenue

$

28,278

$

106,313

$

316,933

$

122,359

$

253,635

Costs and expenses(1)

Cost of revenue

43,168

61,803

128,768

58,157

91,828

Research and development

29,348

80,176

119,004

46,345

111,837

Sales and marketing

6,289

25,988

86,551

34,105

77,697

General and administrative

16,952

65,757

59,693

30,758

35,096

Total costs and expenses

95,757

233,724

394,016

169,365

316,458

Loss from operations

(67,479

)

(127,411

)

(77,083

)

(47,006

)

(62,823

)

Interest income (expense), net

55

(805

)

(2,486

)

(890

)

(2,746

)

Other income (expense), net

(117

)

(1,530

)

399

(12

)

(2,548

)

Loss before income taxes

(67,541

)

(129,746

)

(79,170

)

(47,908

)

(68,117

)

Provision (benefit) for income taxes

(217

)

(1,444

)

229

1,196

1,134

Net loss

$

(67,324

)

$

(128,302

)

$

(79,399

)

$

(49,104

)

$

(69,251

)

Deemed dividend to investors in relation to the tender offer



35,816







Net loss attributable to common stockholders

$

(67,324

)

$

(164,118

)

$

(79,399

)

$

(49,104

)

$

(69,251

)

Weighted-average shares used to compute net loss per share attributable to common stockholders:

Costs and expenses include stock-based compensation expense as follows:

Year Ended December 31,

Six Months EndedJune 30,

2010

2011

2012

2012

2013

(In thousands)

Cost of revenue

$

200

$

1,820

$

800

$

420

$

1,955

Research and development

3,409

33,559

12,622

6,291

24,197

Sales and marketing

249

1,553

1,346

620

4,614

General and administrative

2,073

23,452

10,973

8,796

4,802

Total stock-based compensation

$

5,931

$

60,384

$

25,741

$

16,127

$

35,568

(2)

See Note 9 to our consolidated financial statements for an explanation of the calculations of our pro forma net loss per share attributable to common
stockholders.

(3)

See the section titled Non-GAAP Financial Measures for additional information and a reconciliation of net loss to Adjusted EBITDA and net loss
to non-GAAP net loss.

As of June 30, 2013

Actual

Pro Forma(1)

Pro Formaas
Adjusted(2)(3)

(In thousands)

Consolidated Balance Sheet Data:

Cash and cash equivalents

$

164,509

$

164,509

$

Short-term investments

210,549

210,549

Working capital

382,820

382,820

Property and equipment, net

242,553

242,553

Total assets

964,059

964,059

Total liabilities

255,898

247,163

Class A junior preferred stock

37,106



Convertible preferred stock

835,430



Total stockholders equity (deficit)

(164,375

)

716,896

(1)

The pro forma column in the balance sheet data table above reflects (a) the automatic conversion of all outstanding shares of our Class A junior preferred
stock and our convertible preferred stock into an aggregate of 333,099,000 shares of our common stock, which conversion will occur immediately prior to the completion of this offering, as if such conversion had occurred on June 30, 2013,
(b) the resulting reclassification of the restricted Class A junior preferred stock and preferred stock warrant liability from other long-term liabilities to additional paid-in capital and (c) stock-based compensation expense of
$329.6 million, associated with Pre-2013 RSUs for which the service condition was satisfied as of June 30, 2013, and which we expect to record upon completion of this offering, as further described in the section titled Managements
Discussion and Analysis of Financial Condition and Results of OperationsCritical Accounting Policies and EstimatesStock-Based Compensation.

(2)

The pro forma as adjusted column in the balance sheet data table above gives effect to (a) the pro forma adjustments set forth above, (b) the sale and
issuance by us of shares of our common stock in this offering, based upon the assumed initial public offering price of $ per
share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us and (c) the
filing and effectiveness of our amended and restated certificate of incorporation in Delaware.

(3)

Each $1.00 increase or decrease in the assumed initial public offering price of $ per share, which is the
midpoint of the estimated offering price range set forth on the cover page of this prospectus, would increase or decrease, as applicable, the amount of our cash and cash equivalents, working capital, total assets and total stockholders equity
by $ , assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same, after deducting estimated underwriting discounts and commissions payable by
us. An increase or decrease of 1.0 million shares in the number of shares offered by us would increase or decrease, as applicable, the amount of our cash and cash equivalents, working capital, total assets and total stockholders equity by
$ , assuming an initial public offering price of $ per share, which is the midpoint of the estimated offering price range set forth on the cover page of
this prospectus, after deducting estimated underwriting discounts and commissions payable by us.

Non-GAAP Financial Measures

To supplement our consolidated financial statements presented in accordance with generally accepted accounting principles in the
United States, or GAAP, we consider certain financial measures that are not prepared in accordance with GAAP, including Adjusted EBITDA and non-GAAP net loss.

The following table presents a reconciliation of net loss to non-GAAP net loss for each of the periods indicated:

Year Ended December 31,

Six Months EndedJune 30,

2010

2011

2012

2012

2013

(In thousands)

Reconciliation of Net Loss to Non-GAAP Net Loss

Net loss

$

(67,324

)

$

(128,302

)

$

(79,399

)

$

(49,104

)

$

(69,251

)

Stock-based compensation expense

5,931

60,384

25,741

16,127

35,568

Amortization of acquired intangible assets

7,506

4,697

18,687

10,255

7,178

Income tax effects related to acquisitions

(179

)

(2,312

)

(220

)

490

(383

)

Non-GAAP net loss

$

(54,066

)

$

(65,533

)

$

(35,191

)

$

(22,232

)

$

(26,888

)

We use the non-GAAP financial measures of Adjusted EBITDA and non-GAAP net loss in evaluating our operating results
and for financial and operational decision-making purposes. We believe that Adjusted EBITDA and non-GAAP net loss help identify underlying trends in our business that could otherwise be masked by the effect of the expenses that we exclude in
Adjusted EBITDA and non-GAAP net loss. We believe that Adjusted EBITDA and non-GAAP net loss provide useful information about our operating results, enhance the overall understanding of our past performance and future prospects and allow for greater
transparency with respect to key metrics used by our management in its financial and operational decision-making. We use these measures to establish budgets and operational goals for managing our business and evaluating our performance. We are
presenting the non-GAAP measures of Adjusted EBITDA and non-GAAP net loss to assist investors in seeing our operating results through the eyes of

management, and because we believe that these measures provide an additional tool for investors to use in comparing our core business operating results over multiple periods with other companies
in our industry.

These non-GAAP financial measures should not be considered in isolation from, or as a substitute for, financial
information prepared in accordance with GAAP. There are a number of limitations related to the use of these non-GAAP financial measures rather than net loss, which is the nearest GAAP equivalent of these financial measures. Some of these limitations
are:

Stock-based compensation expense, which is not reflected in these non-GAAP financial measures, has been, and will continue to be for the foreseeable future, a
significant recurring expense in our business and an important part of our compensation strategy;



Adjusted EBITDA does not reflect tax payments that reduce cash available to us;



Adjusted EBITDA excludes depreciation and amortization expense and, although these are non-cash charges, the property and equipment being depreciated and
amortized may have to be replaced in the future; and



The expenses that we exclude in our calculation of these non-GAAP financial measures may differ from the expenses, if any, that our peer companies may exclude
from similarly-titled non-GAAP measures when they report their results of operations.

We have attempted to compensate
for these limitations by providing the nearest GAAP equivalents of these non-GAAP financial measures and describing these GAAP equivalents under the section titled Managements Discussion and Analysis of Financial Condition and Results of
OperationsResults of Operations.

Investing in our common stock involves a high degree of risk. You should carefully consider the risks and uncertainties described below,
together with all of the other information in this prospectus, including Managements Discussion and Analysis of Financial Condition and Results of Operations and our consolidated financial statements and related notes, before
making a decision to invest in our common stock. The risks and uncertainties described below may not be the only ones we face. If any of the risks actually occur, our business, financial condition, operating results and prospects could be materially
and adversely affected. In that event, the market price of our common stock could decline, and you could lose part or all of your investment.

Risks Related to Our Business and Our Industry

If we
fail to grow our user base, or if user engagement or ad engagement on our platform decline, our revenue, business and operating results may be harmed.

The size of our user base and our users level of engagement are critical to our success. We had 218.3 million average MAUs in the three months ended June 30, 2013, which was a 44% increase from
151.4 million average MAUs in the three months ended June 30, 2012. Our financial performance has been and will continue to be significantly determined by our success in growing the number of users and increasing their overall level of
engagement on our platform as well as the number of ad engagements. We anticipate that our user growth rate will slow over time as the size of our user base increases. For example, in general, a higher proportion of Internet users in the United
States uses Twitter than Internet users in other countries and, in the future, we expect our user growth rate in certain international markets, such as Argentina, France, Japan, Russia, Saudi Arabia and South Africa, to continue to be higher than
our user growth rate in the United States. To the extent our user growth rate slows, our success will become increasingly dependent on our ability to increase levels of user engagement and ad engagement on Twitter. We generate a substantial majority
of our revenue based upon engagement by our users with the ads that we display. If people do not perceive our products and services to be useful, reliable and trustworthy, we may not be able to attract users or increase the frequency of their
engagement with our platform and the ads that we display. A number of consumer-oriented websites that achieved early popularity have since seen their user bases or levels of engagement decline, in some cases precipitously. There is no guarantee that
we will not experience a similar erosion of our user base or engagement levels. A number of factors could potentially negatively affect user growth and engagement, including if:



users engage with other products, services or activities as an alternative to ours;



influential users, such as world leaders, government officials, celebrities, athletes, journalists, sports teams, media outlets and brands or certain age
demographics conclude that an alternative product or service is more relevant;



we are unable to convince potential new users of the value and usefulness of our products and services;



there is a decrease in the perceived quality of the content generated by our users;



we fail to introduce new and improved products or services or if we introduce new products or services that are not favorably received;



technical or other problems prevent us from delivering our products or services in a rapid and reliable manner or otherwise affect the user experience;



we are unable to present users with content that is interesting, useful and relevant to them;



users believe that their experience is diminished as a result of the decisions we make with respect to the frequency, relevance and prominence of ads that we
display;



there are user concerns related to privacy and communication, safety, security or other factors;

we are unable to combat spam or other hostile or inappropriate usage on our platform;



there are adverse changes in our products or services that are mandated by, or that we elect to make to address, legislation, regulatory authorities or
litigation, including settlements or consent decrees;



we fail to provide adequate customer service to users; or



we do not maintain our brand image or our reputation is damaged.

If we are unable to increase our user growth or engagement, or if they decline, this could result in our products and services being less attractive to potential new users, as well as advertisers, which
would have a material and adverse impact on our business, financial condition and operating results.

If our users do not continue to contribute
content or their contributions are not valuable to other users, we may experience a decline in the number of users accessing our products and services and user engagement, which could result in the loss of advertisers and revenue.

Our success depends on our ability to provide users of our products and services with valuable content, which in turn depends on
the content contributed by our users. We believe that one of our competitive advantages is the quality, quantity and real-time nature of the content on Twitter, and that access to unique or real-time content is one of the main reasons users visit
Twitter. Our ability to expand into new international markets depends on the availability of relevant local content in those markets. We seek to foster a broad and engaged user community, and we encourage world leaders, government officials,
celebrities, athletes, journalists, sports teams, media outlets and brands to use our products and services to express their views to broad audiences. We also encourage media outlets to use our products and services to distribute their content. If
users, including influential users, do not continue to contribute content to Twitter, and we are unable to provide users with valuable and timely content, our user base and user engagement may decline. Additionally, if we are not able to address
user concerns regarding the safety and security of our products and services or if we are unable to successfully prevent abusive or other hostile behavior on our platform, the size of our user base and user engagement may decline. We rely on the
sale of advertising services for the substantial majority of our revenue. If we experience a decline in the number of users or a decline in user engagement, including as a result of the loss of world leaders, government officials, celebrities,
athletes, journalists, sports teams, media outlets and brands who generate content on Twitter, advertisers may not view our products and services as attractive for their marketing expenditures, and may reduce their spending with us which would harm
our business and operating results.

We generate the substantial majority of our revenue from advertising. The loss of advertising revenue could
harm our business.

The substantial majority of our revenue is currently generated from third parties advertising on Twitter. We
generated 85% and 87% of our revenue from advertising in 2012 and the six months ended June 30, 2013, respectively. We generate substantially all of our advertising revenue through the sale of our three Promoted Products: Promoted Tweets, Promoted
Accounts and Promoted Trends. As is common in the industry, our advertisers do not have long-term advertising commitments with us. In addition, many of our advertisers purchase our advertising services through one of several large advertising agency
holding companies. Advertising agencies and potential new advertisers may view our Promoted Products as experimental and unproven, and we may need to devote additional time and resources to educate them about our products and services. Advertisers
also may choose to reach users through our free products and services, instead of our Promoted Products. Advertisers will not continue to do business with us, or they will reduce the prices they are willing to pay to advertise with us, if we do not
deliver ads in an effective manner, or if they do not believe that their investment in advertising with us will generate a competitive return relative to alternatives, including online, mobile

and traditional advertising platforms. Our advertising revenue could be adversely affected by a number of other factors, including:



decreases in user engagement with Twitter and with the ads on our platform;



if we are unable to demonstrate the value of our Promoted Products to advertisers and advertising agencies or if we are unable to measure the value of our
Promoted Products in a manner which advertisers and advertising agencies find useful;



if our Promoted Products are not cost effective or valuable for certain types of advertisers or if we are unable to develop cost effective or valuable
advertising services for different types of advertisers;



if we are unable to convince advertisers and brands to invest resources in learning to use our products and services and maintaining a brand presence on Twitter;



product or service changes we may make that change the frequency or relative prominence of ads displayed on Twitter or that detrimentally impact revenue in the
near term with the goal of achieving long term benefits;



our inability to increase advertiser demand and inventory;



our inability to increase the relevance of ads shown to users;



our inability to help advertisers effectively target ads, including as a result of the fact that we do not collect extensive private personally identifiable
information directly from our users and that we do not have real-time geographic information for all of our users;



continuing decreases in the cost per ad engagement;



loss of advertising market share to our competitors;



the degree to which users access Twitter content through applications that do not contain our ads;



if we enter into revenue sharing arrangements or other partnerships with third parties;



our new advertising strategies, such as television targeting and real-time video clips embedded in Tweets, do not gain traction;



the impact of new technologies that could block or obscure the display of our ads;



adverse legal developments relating to advertising or measurement tools related to the effectiveness of advertising, including legislative and regulatory
developments, and developments in litigation;



adverse media reports or other negative publicity involving us or other companies in our industry;



our inability to create new products and services that sustain or increase the value of our advertising services to both our advertisers and our users;



the impact of fraudulent clicks or spam on our Promoted Products and our users;



changes in the way our advertising is priced; and



the impact of macroeconomic conditions and conditions in the advertising industry in general.

The occurrence of any of these or other factors could result in a reduction in demand for our ads, which may reduce the prices we receive for our
ads, either of which would negatively affect our revenue and operating results.

If we are unable to compete effectively for users and advertiser
spend, our business and operating results could be harmed.

Competition for users of our products and services is intense.
Although we have developed a new global platform for public self-expression and conversation in real time, we face strong competition in our

business. We compete against many companies to attract and engage users, including companies which have greater financial resources and substantially larger user bases, such as Facebook
(including Instagram), Google, LinkedIn, Microsoft and Yahoo!, which offer a variety of Internet and mobile device-based products, services and content. For example, Facebook operates a social networking site with significantly more users than
Twitter and has been introducing features similar to those of Twitter. In addition, Google may use its strong position in one or more markets to gain a competitive advantage over us in areas in which we operate, including by integrating competing
features into products or services they control. As a result, our competitors may acquire and engage users at the expense of the growth or engagement of our user base, which would negatively affect our business. We also compete against smaller
companies, such as Sina Weibo, LINE and Kakao, each of which is based in Asia.

We believe that our ability to compete effectively for
users depends upon many factors both within and beyond our control, including:



the popularity, usefulness, ease of use, performance and reliability of our products and services compared to those of our competitors;



the amount, quality and timeliness of content generated by our users;



the timing and market acceptance of our products and services;



the continued adoption of our products and services internationally;



our ability, and the ability of our competitors, to develop new products and services and enhancements to existing products and services;



the frequency and relative prominence of the ads displayed by us or our competitors;



our ability to establish and maintain relationships with platform partners that integrate with our platform;



changes mandated by, or that we elect to make to address, legislation, regulatory authorities or litigation, including settlements and consent decrees, some of
which may have a disproportionate effect on us;



the application of antitrust laws both in the United States and internationally;

acquisitions or consolidation within our industry, which may result in more formidable competitors; and



our reputation and the brand strength relative to our competitors.

We also face significant competition for advertiser spend. The substantial majority of our revenue is currently generated through ads on Twitter, and we compete against online and mobile businesses, including those
referenced above, and traditional media outlets, such as television, radio and print, for advertising budgets. In order to grow our revenue and improve our operating results, we must increase our share of spending on advertising relative to our
competitors, many of which are larger companies that offer more traditional and widely accepted advertising products. In addition, some of our larger competitors have substantially broader product or service offerings and leverage their
relationships based on other products or services to gain additional share of advertising budgets.

We believe that our ability to
compete effectively for advertiser spend depends upon many factors both within and beyond our control, including:



the size and composition of our user base relative to those of our competitors;

the timing and market acceptance of our advertising services, and those of our competitors;



our marketing and selling efforts, and those of our competitors;



the pricing for our Promoted Products relative to the advertising products and services of our competitors;



the return our advertisers receive from our advertising services, and those of our competitors; and



our reputation and the strength of our brand relative to our competitors.

In recent years, there have been significant acquisitions and consolidation by and among our actual and potential competitors. We anticipate this
trend of consolidation will continue, which will present heightened competitive challenges for our business. Acquisitions by our competitors may result in reduced functionality of our products and services. For example, following Facebooks
acquisition of Instagram, Facebook disabled Instagrams photo integration with Twitter such that Instagram photos are no longer viewable within Tweets and users are now re-directed to Instagram to view Instagram photos through a link within a
Tweet. As a result, our users may be less likely to click on links to Instagram photos in Tweets, and Instagram users may be less likely to tweet or remain active users of Twitter. Any similar elimination of integration with Twitter in the future,
whether by Facebook or others, may adversely impact our business and operating results.

Consolidation may also enable our larger
competitors to offer bundled or integrated products that feature alternatives to our platform. Reduced functionality of our products and services, or our competitors ability to offer bundled or integrated products that compete directly with
us, may cause our user growth, user engagement and ad engagement to decline and advertisers to reduce their spend with us.

If we are
not able to compete effectively for users and advertiser spend our business and operating results would be materially and adversely affected.

Our
operating results may fluctuate from quarter to quarter, which makes them difficult to predict.

Our quarterly operating results
have fluctuated in the past and will fluctuate in the future. As a result, our past quarterly operating results are not necessarily indicators of future performance. Our operating results in any given quarter can be influenced by numerous factors,
many of which we are unable to predict or are outside of our control, including:



our ability to grow our user base and user engagement;



our ability to attract and retain advertisers;



the occurrence of planned significant events, such as the Super Bowl, or unplanned significant events, such as natural disasters and political revolutions;



fluctuations in spending by our advertisers, including as a result of seasonality and extraordinary news events, or other factors;



the number of ad engagements by users;



the pricing of our ads and other products and services;



the development and introduction of new products or services or changes in features of existing products or services;

system failures resulting in the inaccessibility of our products and services;



breaches of security or privacy, and the costs associated with remediating any such breaches;



adverse litigation judgments, settlements or other litigation-related costs, and the fees associated with investigating and defending claims;



changes in the legislative or regulatory environment, including with respect to security, privacy or enforcement by government regulators, including fines,
orders or consent decrees;



fluctuations in currency exchange rates and changes in the proportion of our revenue and expenses denominated in foreign currencies;



changes in U.S. generally accepted accounting principles; and



changes in global business or macroeconomic conditions.

Given our limited operating history and the rapidly evolving markets in which we compete, our historical operating results may not be useful to you in predicting our future operating results. We believe our rapid
growth may understate the potential seasonality of our business. As our revenue growth rate slows, we expect that the seasonality in our business may become more pronounced and may in the future cause our operating results to fluctuate. For example,
advertising spending is traditionally seasonally strong in the fourth quarter of each year and we believe that this seasonality affects our quarterly results, which generally reflect higher sequential advertising revenue growth from the third to
fourth quarter compared to sequential advertising revenue growth from the fourth quarter to the subsequent first quarter. In addition, global economic concerns continue to create uncertainty and unpredictability and add risk to our future outlook.
An economic downturn in any particular region in which we do business or globally could result in reductions in advertising revenue, as our advertisers reduce their advertising budgets, and other adverse effects that could harm our operating
results.

User growth and engagement depend upon effective interoperation with operating systems, networks, devices, web browsers and standards
that we do not control.

We make our products and services available across a variety of operating systems and through websites.
We are dependent on the interoperability of our products and services with popular devices, desktop and mobile operating systems and web browsers that we do not control, such as Mac OS, Windows, Android, iOS, Chrome and Firefox. Any changes in such
systems, devices or web browsers that degrade the functionality of our products and services or give preferential treatment to competitive products or services could adversely affect usage of our products and services. Further, if the number of
platforms for which we develop our product expands, it will result in an increase in our operating expenses. In order to deliver high quality products and services, it is important that our products and services work well with a range of operating
systems, networks, devices, web browsers and standards that we do not control. In addition, because a majority of our users access our products and services through mobile devices, we are particularly dependent on the interoperability of our
products and services with mobile devices and operating systems. We may not be successful in developing relationships with key participants in the mobile industry or in developing products or services that operate effectively with these operating
systems, networks, devices, web browsers and standards. In the event that it is difficult for our users to access and use our products and services, particularly on their mobile devices, our user growth and engagement could be harmed, and our
business and operating results could be adversely affected.

If we fail to expand effectively in international markets, our revenue and our business will be harmed.

We may not be able to monetize our products and services internationally as effectively as in the United States as a result of
competition, advertiser demand, differences in the digital advertising market and digital advertising conventions, as well as differences in the way that users in different countries access or utilize our products and services. Differences in the
competitive landscape in international markets may impact our ability to monetize our products and services. For example, in South Korea we face intense competition from a messaging service offered by Kakao, which offers some of the same
communication features as Twitter. The existence of a well-established competitor in an international market may adversely affect our ability to increase our user base, attract advertisers and monetize our products in such market. We may also
experience differences in advertiser demand in international markets. For example, during times of political upheaval, advertisers may choose not to advertise on Twitter. Certain international markets are also not as familiar with digital
advertising in general, or in new forms of digital advertising such as our Promoted Products. Further, we face challenges in providing certain advertising products, features or analytics in certain international markets, such as the European Union,
due to government regulation. Our products and services may also be used differently abroad than in the United States. In particular, in certain international markets where Internet access is not as rapid or reliable as in the United States, users
tend not to take advantage of certain features of our products and services, such as rich media included in Tweets. Additionally, in certain emerging markets, such as India, many users access our products and services through feature phones with
limited functionality, rather than through smartphones, our website or desktop applications. This limits our ability to deliver certain features to those users and may limit the ability of advertisers to deliver compelling advertisements to users in
these markets which may result in reduced ad engagements which would adversely affect our business and operating results.

If our
revenue from our international operations, and particularly from operations in the countries and regions on which we have focused our spending, does not exceed the expense of establishing and maintaining these operations, our business and operating
results will suffer. In addition, our user base may expand more rapidly in international regions where we are less successful in monetizing our products and services. As our user base continues to expand internationally, we will need to increase
revenue from the activity generated by our international users in order to grow our business. For example, users outside the United States constituted 77% of our average MAUs in the three months ended June 30, 2013, but our international revenue, as
determined based on the billing location of our advertisers, was only 25% of our consolidated revenue in the three months ended June 30, 2013. Our inability to successfully expand internationally could adversely affect our business, financial
condition and operating results.

We have a limited operating history in a new and unproven market for our platform, which makes it difficult to
evaluate our future prospects and may increase the risk that we will not be successful.

We have developed a global platform for
public self-expression and conversation in real time, and the market for our products and services is relatively new and may not develop as expected, if at all. People who are not our users may not understand the value of our products and services
and new users may initially find our product confusing. There may be a perception that our products and services are only useful to users who tweet, or to influential users with large audiences. Convincing potential new users of the value of our
products and services is critical to increasing our user base and to the success of our business.

We have a limited operating history, and only began to generate revenue in 2009 and we started to sell
our Promoted Products in 2010, which makes it difficult to effectively assess our future prospects or forecast our future results. You should consider our business and prospects in light of the risks and challenges we encounter or may encounter in
this developing and rapidly evolving market. These risks and challenges include our ability to, among other things:

convince advertisers of the benefits of our Promoted Products compared to alternative forms of advertising;

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develop and deploy new features, products and services;

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successfully compete with other companies, some of which have substantially greater resources and market power than us, that are currently in, or may in the
future enter, our industry, or duplicate the features of our products and services;

If we fail to educate potential users and potential advertisers about the value of our products and services, if the market for our platform does
not develop as we expect or if we fail to address the needs of this market, our business will be harmed. We may not be able to successfully address these risks and challenges or others. Failure to adequately address these risks and challenges could
harm our business and cause our operating results to suffer.

We have incurred significant operating losses in the past, and we may not be able to
achieve or subsequently maintain profitability.

Since our inception, we have incurred significant operating losses, and, as of
June 30, 2013, we had an accumulated deficit of $418.6 million. Although our revenue has grown rapidly, increasing from $28.3 million in 2010 to $316.9 million in 2012, we expect that our revenue growth rate will slow in the future as
a result of a variety of factors, including the gradual slow down in the growth rate of our user base. We believe that our future revenue growth will depend on, among other factors, our ability to attract new users, increase user engagement and ad
engagement, increase our brand awareness, compete effectively, maximize our sales efforts, demonstrate a positive return on investment for advertisers, successfully develop new products and services and expand internationally. Accordingly, you
should not rely on the revenue growth of any prior quarterly or annual period as an indication of our future performance. We also expect our costs to increase in future periods as we continue to expend substantial financial resources on:

strategic opportunities, including commercial relationships and acquisitions; and

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general administration, including personnel costs and legal and accounting expenses related to being a public company.

These investments may not result in increased revenue or growth in our business.

In addition, we have granted stock options and RSUs to our employees. RSUs granted to domestic employees before February 2013 and all RSUs granted to international employees, or the Pre-2013 RSUs, vest upon the
satisfaction of both a service condition and a performance condition. The service condition for a majority of the Pre-2013 RSUs is satisfied over a period of four years. The performance condition will be satisfied on the earlier of (i) the date that
is the earlier of (x) six months after the effective date of this offering or (y) March 8th of the calendar year following the effective date of this offering (which we may elect to accelerate to February 15th); and (ii) the date of a change in
control. As of June 30, 2013, no stock-based compensation expense had been recognized for the Pre-2013 RSUs because a qualifying event as described above was not probable. In the quarter in which this offering is completed, we will begin recording
stock-based compensation expense based on the grant-date fair value of the Pre-2013 RSUs using the accelerated attribution method, net of estimated forfeitures. If this offering had been completed on June 30, 2013, we would have recorded $329.6
million of cumulative stock-based compensation expense related to the Pre-2013 RSUs on that date, and an additional $234.2 million of unrecognized stock-based compensation expense related to the Pre-2013 RSUs, net of estimated forfeitures, would be
recognized over a weighted-average period of approximately three years. In addition to stock-based compensation expense associated with the Pre-2013 RSUs, as of June 30, 2013, we had unrecognized stock-based compensation expense of approximately
$296.7 million related to other outstanding equity awards, after giving effect to estimated forfeitures, which we expect to recognize over a weighted-average period of approximately four years. Further, we made grants of equity awards after June 30,
2013, and we have unrecognized stock-based compensation expense of $452.9 million related to such equity awards, after giving effect to estimated forfeitures, which we expect to recognize over a weighted-average period of approximately four years.
Following the completion of this offering, the stock-based compensation expense related to Pre-2013 RSUs and other outstanding equity awards will have a significant negative impact on our ability to achieve profitability on a GAAP basis in 2013 and
2014.

If we are unable to generate adequate revenue growth and to manage our expenses, we may continue to incur significant losses in
the future and may not be able to achieve or maintain profitability.

Our business depends on continued and unimpeded access to our products and
services on the Internet by our users and advertisers. If we or our users experience disruptions in Internet service or if Internet service providers are able to block, degrade or charge for access to our products and services, we could incur
additional expenses and the loss of users and advertisers.

We depend on the ability of our users and advertisers to access the
Internet. Currently, this access is provided by companies that have significant market power in the broadband and Internet access marketplace, including incumbent telephone companies, cable companies, mobile communications companies,
government-owned service providers, device manufacturers and operating system providers, any of whom could take actions that degrade, disrupt or increase the cost of user access to our products or services, which would, in turn, negatively impact
our business. For example, access to Twitter is blocked in China. The adoption of any laws or regulations that adversely

affect the growth, popularity or use of the Internet, including laws or practices limiting Internet neutrality, could decrease the demand for, or the usage of, our products and services, increase
our cost of doing business and adversely affect our operating results. We also rely on other companies to maintain reliable network systems that provide adequate speed, data capacity and security to us and our users. As the Internet continues to
experience growth in the number of users, frequency of use and amount of data transmitted, the Internet infrastructure that we and our users rely on may be unable to support the demands placed upon it. The failure of the Internet infrastructure that
we or our users rely on, even for a short period of time, could undermine our operations and harm our operating results.

Our new products,
services and initiatives and changes to existing products, services and initiatives could fail to attract users and advertisers or generate revenue.

Our ability to increase the size and engagement of our user base, attract advertisers and generate revenue will depend in part on our ability to create successful new products and services, both independently and
in conjunction with third parties. We may introduce significant changes to our existing products and services or develop and introduce new and unproven products and services, including technologies with which we have little or no prior development
or operating experience. For example, in 2013, we introduced Vine, a mobile application that enables users to create and distribute videos that are up to six seconds in length, and #Music, a mobile application that helps users discover new music and
artists based on Twitter data. If new or enhanced products or services fail to engage users and advertisers, we may fail to attract or retain users or to generate sufficient revenue or operating profit to justify our investments, and our business
and operating results could be adversely affected. In addition, we have launched and expect to continue to launch strategic initiatives, such as the Nielsen Twitter TV Rating, that do not directly generate revenue but which we believe will enhance
our attractiveness to users and advertisers. In the future, we may invest in new products, services and initiatives to generate revenue, but there is no guarantee these approaches will be successful. We may not be successful in future efforts to
generate revenue from our new products or services. If our strategic initiatives do not enhance our ability to monetize our existing products and services or enable us to develop new approaches to monetization, we may not be able to maintain or grow
our revenue or recover any associated development costs and our operating results could be adversely affected.

Spam could diminish the user
experience on our platform, which could damage our reputation and deter our current and potential users from using our products and services.

Spam on Twitter refers to a range of abusive activities that are prohibited by our terms of service and is generally defined as unsolicited, repeated actions that negatively impact other users with the
general goal of drawing user attention to a given account, site, product or idea. This includes posting large numbers of unsolicited mentions of a user, duplicate Tweets, misleading links (e.g., to malware or click-jacking pages) or other false or
misleading content, and aggressively following and un-following accounts, adding users to lists, sending invitations, retweeting and favoriting Tweets to inappropriately attract attention. Our terms of service also prohibit the creation of serial or
bulk accounts, both manually or using automation, for disruptive or abusive purposes, such as to tweet spam or to artificially inflate the popularity of users seeking to promote themselves on Twitter. Although we continue to invest resources to
reduce spam on Twitter, we expect spammers will continue to seek ways to act inappropriately on our platform. In addition, we expect that increases in the number of users on our platform will result in increased efforts by spammers to misuse our
platform. We continuously combat spam, including by suspending or terminating accounts we believe to be spammers and launching algorithmic changes focused on curbing abusive activities. Our actions to combat spam require the diversion of significant
time and focus of our engineering team from improving our products and services. If spam increases on Twitter, this could hurt our reputation for delivering relevant content or reduce user growth and user engagement and result in continuing
operational cost to us.

If we fail to effectively manage our growth, our business and operating results could be harmed.

We continue to experience rapid growth in our headcount and operations, which will continue to place significant demands on our
management, operational and financial infrastructure. As of June 30, 2013, we had approximately 2,000 employees, an increase of over 1,800 employees since January 1, 2010. We intend to continue to make substantial investments to expand our
operations, research and development, sales and marketing and general and administrative organizations, as well as our international operations. We face significant competition for employees, particularly engineers, designers and product managers,
from other Internet and high-growth companies, which include both publicly-traded and privately-held companies, and we may not be able to hire new employees quickly enough to meet our needs. To attract highly skilled personnel, we have had to offer,
and believe we will need to continue to offer, highly competitive compensation packages. In addition, as we have grown, we have significantly expanded our operating lease commitments. As we continue to grow, we are subject to the risks of
over-hiring, over-compensating our employees and over-expanding our operating infrastructure, and to the challenges of integrating, developing and motivating a rapidly growing employee base in various countries around the world. In addition, we may
not be able to innovate or execute as quickly as a smaller, more efficient organization. If we fail to effectively manage our hiring needs and successfully integrate our new hires, our efficiency and ability to meet our forecasts and our employee
morale, productivity and retention could suffer, and our business and operating results could be adversely affected.

Providing our
products and services to our users is costly and we expect our expenses to continue to increase in the future as we broaden our user base and increase user engagement, as users increase the amount of content they contribute, and as we develop and
implement new features, products and services that require more infrastructure, such as our mobile video product, Vine. In addition, our operating expenses, such as our research and development expenses and sales and marketing expenses, have grown
rapidly as we have expanded our business. Historically, our costs have increased each year due to these factors and we expect to continue to incur increasing costs to support our anticipated future growth. We expect to continue to invest in our
infrastructure in order to enable us to provide our products and services rapidly and reliably to users around the world, including in countries where we do not expect significant near-term monetization. Continued growth could also strain our
ability to maintain reliable service levels for our users and advertisers, develop and improve our operational, financial, legal and management controls, and enhance our reporting systems and procedures. As a public company we will incur significant
legal, accounting and other expenses that we did not incur as a private company. Our expenses may grow faster than our revenue, and our expenses may be greater than we anticipate. Managing our growth will require significant expenditures and
allocation of valuable management resources. If we fail to achieve the necessary level of efficiency in our organization as it grows, our business, operating results and financial condition would be harmed.

Our business and operating results may be harmed by a disruption in our service, or by our failure to timely and effectively scale and adapt our existing
technology and infrastructure.

One of the reasons people come to Twitter is for real-time information. We have experienced, and
may in the future experience, service disruptions, outages and other performance problems due to a variety of factors, including infrastructure changes, human or software errors, hardware failure, capacity constraints due to an overwhelming number
of people accessing our products and services simultaneously, computer viruses and denial of service or fraud or security attacks. Although we are investing significantly to improve the capacity, capability and reliability of our infrastructure, we
are not currently serving traffic equally through our co-located data centers that support our platform. Accordingly, in the event of a significant issue at the data center supporting most of our network traffic,

some of our products and services may become inaccessible to the public or the public may experience difficulties accessing our products and services. For example, in July 2012, due to the
failure of two parallel systems at nearly the same time in one of our data centers, Twitter became inaccessible for approximately two hours. Any disruption or failure in our infrastructure could hinder our ability to handle existing or increased
traffic on our platform, which could significantly harm our business.

As the number of our users increases and our users generate more
content, including photos and videos hosted by Twitter, we may be required to expand and adapt our technology and infrastructure to continue to reliably store, serve and analyze this content. It may become increasingly difficult to maintain and
improve the performance of our products and services, especially during peak usage times, as our products and services become more complex and our user traffic increases. In addition, because we lease our data center facilities, we cannot be assured
that we will be able to expand our data center infrastructure to meet user demand in a timely manner, or on favorable economic terms. If our users are unable to access Twitter or we are not able to make information available rapidly on Twitter,
users may seek other channels to obtain the information, and may not return to Twitter or use Twitter as often in the future, or at all. This would negatively impact our ability to attract users and advertisers and increase engagement of our users.
We expect to continue to make significant investments to maintain and improve the capacity, capability and reliability of our infrastructure. To the extent that we do not effectively address capacity constraints, upgrade our systems as needed and
continually develop our technology and infrastructure to accommodate actual and anticipated changes in technology, our business and operating results may be harmed.

Action by governments to restrict access to our products and services or censor Twitter content could harm our business and operating results.

Governments have sought, and may in the future seek, to censor content available through our products and services, restrict access to our products
and services from their country entirely or impose other restrictions that may affect the accessibility of our products and services for an extended period of time or indefinitely. For example, domestic Internet service providers in China have
blocked access to Twitter, and other countries, including Iran, Libya, Pakistan and Syria, have intermittently restricted access to Twitter, and we believe that access to Twitter has been blocked in these countries primarily for political reasons.
In addition, governments in other countries may seek to restrict access to our products and services if they consider us to be in violation of their laws. In the event that access to our products and services is restricted, in whole or in part, in
one or more countries or our competitors are able to successfully penetrate geographic markets that we cannot access, our ability to retain or increase our user base and user engagement may be adversely affected, and our operating results may be
harmed.

If we are unable to maintain and promote our brand, our business and operating results may be harmed.

We believe that maintaining and promoting our brand is critical to expanding our base of users and advertisers. Maintaining and promoting our brand
will depend largely on our ability to continue to provide useful, reliable and innovative products and services, which we may not do successfully. We may introduce new features, products, services or terms of service that users, platform partners or
advertisers do not like, which may negatively affect our brand. Additionally, the actions of platform partners may affect our brand if users do not have a positive experience using third-party applications or websites integrated with Twitter or that
make use of Twitter content. Our brand may also be negatively affected by the actions of users that are hostile or inappropriate to other people, by users impersonating other people, by users identified as spam, by users introducing excessive
amounts of spam on our platform or by third parties obtaining control over users accounts. For example, in April 2013, attackers obtained the credentials to the Twitter account of the Associated Press news service

through a phishing attack targeting Associated Press employees. The attackers posted an erroneous Tweet from the Associated Press account reporting that there had been explosions at
the White House, triggering a stock market decline, and focusing media attention on our brand and security efforts. Maintaining and enhancing our brand may require us to make substantial investments and these investments may not achieve the desired
goals. If we fail to successfully promote and maintain our brand or if we incur excessive expenses in this effort, our business and operating results could be adversely affected.

Negative publicity could adversely affect our business and operating results.

We
receive a high degree of media coverage around the world. Negative publicity about our company, including about our product quality and reliability, changes to our products and services, privacy and security practices, litigation, regulatory
activity, the actions of our users or user experience with our products and services, even if inaccurate, could adversely affect our reputation and the confidence in and the use of our products and services. For example, service outages on Twitter
typically result in widespread media reports. Such negative publicity could also have an adverse effect on the size, engagement and loyalty of our user base and result in decreased revenue, which could adversely affect our business and operating
results.

Our future performance depends in part on support from platform partners and data partners.

We believe user engagement with our products and services depends in part on the availability of applications and content generated by platform
partners. Beginning in 2012, we launched Twitter Cards, which allow platform partners to ensure that whenever they or any user tweets from their websites or applications, the Tweet will automatically include rich content like a photo, a video, a
sound clip, an article summary or information about a product, and make it instantly accessible to any other user on Twitter. Twitter Cards allow platform partners to create lightweight interactive applications to promote their content or their
products. The availability and development of these applications and content depends on platform partners perceptions and analysis of the relative benefits of developing applications and content for our products and services. If platform
partners focus their efforts on other platforms, the availability and quality of applications and content for our products and services may suffer. There is no assurance that platform partners will continue to develop and maintain applications and
content for our products and services. If platform partners cease to develop and maintain applications and content for our products and services, user engagement may decline. In addition, we generate revenue from licensing our historical and
real-time data to third parties. If any of these relationships are terminated or not renewed, or if we are unable to enter into similar relationships in the future, our operating results could be adversely affected.

We focus on product innovation and user engagement rather than short-term operating results.

We encourage employees to quickly develop and help us launch new and innovative features. We focus on improving the user experience for our products
and services and on developing new and improved products and services for the advertisers on our platform. We prioritize innovation and the experience for users and advertisers on our platform over short-term operating results. We frequently make
product and service decisions that may reduce our short-term operating results if we believe that the decisions are consistent with our goals to improve the user experience and performance for advertisers, which we believe will improve our operating
results over the long term. These decisions may not be consistent with the short-term expectations of investors and may not produce the long-term benefits that we expect, in which case our user growth and user engagement, our relationships with
advertisers and our business and operating results could be harmed. In addition, our focus on the user experience may negatively impact our relationships with our existing or prospective advertisers. This could result in a loss of advertisers, which
could harm our revenue and operating results.

Our international operations are subject to increased challenges and risks.

We have offices around the world and our products and services are available in multiple languages. We expect to continue to expand our
international operations in the future by opening offices in new jurisdictions and expanding our offerings in new languages. However, we have limited operating history outside the United States, and our ability to manage our business and conduct our
operations internationally requires considerable management attention and resources and is subject to the particular challenges of supporting a rapidly growing business in an environment of multiple languages, cultures, customs, legal and regulatory
systems, alternative dispute systems and commercial markets. International expansion has required and will continue to require us to invest significant funds and other resources. Operating internationally subjects us to new risks and may increase
risks that we currently face, including risks associated with:

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recruiting and retaining talented and capable employees in foreign countries and maintaining our company culture across all of our offices;

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providing our products and services and operating across a significant distance, in different languages and among different cultures, including the potential
need to modify our products, services, content and features to ensure that they are culturally relevant in different countries;

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increased competition from local websites, mobile applications and services that provide real-time communications, such as Sina Weibo in China, LINE in Japan and
Kakao in South Korea, which have expanded and may continue to expand their geographic footprint;

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differing and potentially lower levels of user growth, user engagement and ad engagement in new and emerging geographies;

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different levels of advertiser demand;

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greater difficulty in monetizing our products and services;

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compliance with applicable foreign laws and regulations, including laws and regulations with respect to privacy, consumer protection, spam and content, and the
risk of penalties to our users and individual members of management if our practices are deemed to be out of compliance;

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longer payment cycles in some countries;

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credit risk and higher levels of payment fraud;

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operating in jurisdictions that do not protect intellectual property rights to the same extent as the United States;

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compliance with anti-bribery laws including, without limitation, compliance with the Foreign Corrupt Practices Act and the U.K. Bribery Act, including by our
business partners;

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currency exchange rate fluctuations;

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foreign exchange controls that might require significant lead time in setting up operations in certain geographic territories and might prevent us from
repatriating cash earned outside the United States;

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political and economic instability in some countries;

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double taxation of our international earnings and potentially adverse tax consequences due to changes in the tax laws of the United States or the foreign
jurisdictions in which we operate; and

Our products and services may contain undetected software errors, which could harm our business and operating
results.

Our products and services incorporate complex software and we encourage employees to quickly develop and help us launch
new and innovative features. Our software has contained, and may now or in the future contain, errors, bugs or vulnerabilities. For example, we experienced a service outage in June 2012 during which Twitter service was inaccessible for approximately
two hours as a result of a cascading software bug in one of our infrastructure components. Some errors in our software code may only be discovered after the product or service has been released. Any errors, bugs or vulnerabilities discovered in our
code after release could result in damage to our reputation, loss of users, loss of platform partners, loss of advertisers or advertising revenue or liability for damages, any of which could adversely affect our business and operating results.

Our business is subject to complex and evolving U.S. and foreign laws and regulations. These laws and regulations are subject to change and
uncertain interpretation, and could result in claims, changes to our business practices, monetary penalties, increased cost of operations or declines in user growth, user engagement or ad engagement, or otherwise harm our business.

We are subject to a variety of laws and regulations in the United States and abroad that involve matters central to our
business, including privacy, rights of publicity, data protection, content regulation, intellectual property, competition, protection of minors, consumer protection and taxation. Many of these laws and regulations are still evolving and being tested
in courts and could be interpreted or applied in ways that could harm our business, particularly in the new and rapidly evolving industry in which we operate. The introduction of new products or services may subject us to additional laws and
regulations. In addition, foreign data protection, privacy, consumer protection, content regulation and other laws and regulations are often more restrictive than those in the United States. In particular, the European Union and its member states
traditionally have taken broader views as to types of data that are subject to privacy and data protection, and have imposed greater legal obligations on companies in this regard. A number of proposals are pending before federal, state and foreign
legislative and regulatory bodies that could significantly affect our business. For example, regulation relating to the 1995 European Union Data Protection Directive is currently being considered by European legislative bodies that may include more
stringent operational requirements for entities processing personal information and significant penalties for non-compliance. Similarly, there have been a number of recent legislative proposals in the United States, at both the federal and state
level, that would impose new obligations in areas such as privacy and liability for copyright infringement by third parties. The U.S. government, including the Federal Trade Commission, or the FTC, and the Department of Commerce, has announced that
it is reviewing the need for greater regulation for the collection of information concerning user behavior on the Internet, including regulation aimed at restricting certain online tracking and targeted advertising practices. Additionally, recent
amendments to U.S. patent laws may affect the ability of companies, including us, to protect their innovations and defend against claims of patent infringement. We currently allow use of our platform without the collection of extensive personal
information, such as age. We may experience additional pressure to expand our collection of personal information in order to comply with new and additional regulatory demands or we may independently decide to do so. Having additional personal
information may subject us to additional regulation. Further, it is difficult to predict how existing laws and regulations will be applied to our business and the new laws and regulations to which we may become subject, and it is possible that they
may be interpreted and applied in a manner that is inconsistent with our practices. These existing and proposed laws and regulations can be costly to comply with and can delay or impede the development of new products and services, result in
negative publicity, significantly increase our operating costs, require significant time and attention of management and technical personnel and subject us to inquiries or investigations, claims or other remedies, including fines or demands that we
modify or cease existing business practices.

Regulatory investigations and settlements could cause us to incur additional expenses or change our business
practices in a manner materially adverse to our business.

We have been subject to regulatory investigations in the past, and
expect to continue to be subject to regulatory scrutiny as our business grows and awareness of our brand increases. In March 2011, to resolve an investigation into various incidents, we entered into a settlement agreement with the FTC that, among
other things, requires us to establish an information security program designed to protect non-public consumer information and also requires that we obtain biennial independent security assessments. The obligations under the settlement agreement
remain in effect until the latter of March 2, 2031, or the date 20 years after the date, if any, on which the U.S. government or the FTC files a complaint in federal court alleging any violation of the order. We expect to continue to be the
subject of regulatory inquiries, investigations and audits in the future by the FTC and other regulators around the world.

It is
possible that a regulatory inquiry, investigation or audit might result in changes to our policies or practices, and may cause us to incur substantial costs or could result in reputational harm, prevent us from offering certain products, services,
features or functionalities, cause us to incur substantial costs or require us to change our business practices in a manner materially adverse to our business. Violation of existing or future regulatory orders, settlements or consent decrees could
subject us to substantial monetary fines and other penalties that could negatively affect our financial condition and operating results.

Even
though Twitter is a global platform for public self-expression and conversation, user trust regarding privacy is important to the growth of users and the increase in user engagement on our platform, and privacy concerns relating to our products and
services could damage our reputation and deter current and potential users and advertisers from using Twitter.

From time to
time, concerns have been expressed by governments, regulators and others about whether our products, services or practices compromise the privacy of users and others. Concerns about, governmental or regulatory actions involving our practices with
regard to the collection, use, disclosure or security of personal information or other privacy-related matters, even if unfounded, could damage our reputation, cause us to lose users and advertisers and adversely affect our operating results. While
we strive to comply with applicable data protection laws and regulations, as well as our own posted privacy policies and other obligations we may have with respect to privacy and data protection, the failure or perceived failure to comply may
result, and in some cases has resulted, in inquiries and other proceedings or actions against us by governments, regulators or others, as well as negative publicity and damage to our reputation and brand, each of which could cause us to lose users
and advertisers, which could have an adverse effect on our business.

Any systems failure or compromise of our security that results in
the unauthorized access to or release of our users or advertisers data could significantly limit the adoption of our products and services, as well as harm our reputation and brand and, therefore, our business. We expect to continue to
expend significant resources to protect against security breaches. The risk that these types of events could seriously harm our business is likely to increase as we expand the number of products and services we offer, increase the size of our user
base and operate in more countries.

Governments and regulators around the world are considering a number of legislative and regulatory
proposals concerning data protection. In addition, the interpretation and application of consumer and data protection laws or regulations in the United States, Europe and elsewhere are often uncertain and in flux, and in some cases, laws or
regulations in one country may be inconsistent with, or contrary to, those of another country. It is possible that these laws and regulations may be interpreted and applied in a manner that is inconsistent with our practices. If so, in addition to
the possibility of fines, this could result in an order requiring that we change our practices, which could have an adverse effect on our business and operating results. Complying with new laws and regulations could cause us to incur substantial
costs or require us to change our business practices in a manner materially adverse to our business.

If our security measures are breached, or if our products and services are subject to attacks that degrade or
deny the ability of users to access our products and services, our products and services may be perceived as not being secure, users and advertisers may curtail or stop using our products and services and our business and operating results could be
harmed.

Our products and services involve the storage and transmission of users and advertisers information, and
security breaches expose us to a risk of loss of this information, litigation and potential liability. We experience cyber-attacks of varying degrees on a regular basis, and as a result, unauthorized parties have obtained, and may in the future
obtain, access to our data or our users or advertisers data. For example, in February 2013, we disclosed that sophisticated unknown third parties had attacked our systems and may have had access to limited information for approximately
250,000 users. Our security measures may also be breached due to employee error, malfeasance or otherwise. Additionally, outside parties may attempt to fraudulently induce employees, users or advertisers to disclose sensitive information in order to
gain access to our data or our users or advertisers data or accounts, or may otherwise obtain access to such data or accounts. Since our users and advertisers may use their Twitter accounts to establish and maintain online identities,
unauthorized communications from Twitter accounts that have been compromised may damage their reputations and brands as well as ours. Any such breach or unauthorized access could result in significant legal and financial exposure, damage to our
reputation and a loss of confidence in the security of our products and services that could have an adverse effect on our business and operating results. Because the techniques used to obtain unauthorized access, disable or degrade service or
sabotage systems change frequently and often are not recognized until launched against a target, we may be unable to anticipate these techniques or to implement adequate preventative measures. If an actual or perceived breach of our security occurs,
the market perception of the effectiveness of our security measures could be harmed, we could lose users and advertisers and we may incur significant legal and financial exposure, including legal claims and regulatory fines and penalties. Any of
these actions could have a material and adverse effect on our business, reputation and operating results.

We may face lawsuits or incur liability
as a result of content published or made available through our products and services.

We have faced and will continue to face
claims relating to content that is published or made available through our products and services or third party products or services. In particular, the nature of our business exposes us to claims related to defamation, intellectual property rights,
rights of publicity and privacy, illegal content, content regulation and personal injury torts. The law relating to the liability of providers of online products or services for activities of their users remains somewhat unsettled, both within the
United States and internationally. This risk may be enhanced in certain jurisdictions outside the United States where we may be less protected under local laws than we are in the United States. In addition, the public nature of communications on our
network exposes us to risks arising from the creation of impersonation accounts intended to be attributed to our users or advertisers. We could incur significant costs investigating and defending these claims. If we incur costs or liability as a
result of these events occurring, our business, financial condition and operating results could be adversely affected.

Our intellectual property
rights are valuable, and any inability to protect them could reduce the value of our products, services and brand.

Our trade
secrets, trademarks, copyrights, patents and other intellectual property rights are important assets for us. We rely on, and expect to continue to rely on, a combination of confidentiality and license agreements with our employees, consultants and
third parties with whom we have relationships, as well as trademark, trade dress, domain name, copyright, trade secret and patent laws, to protect our brand and other intellectual property rights. However, various events outside of our control pose
a threat to our intellectual property rights, as well as to our products, services and

technologies. For example, we may fail to obtain effective intellectual property protection, or effective intellectual property protection may not be available in every country in which our
products and services are available. Also, the efforts we have taken to protect our intellectual property rights may not be sufficient or effective, and any of our intellectual property rights may be challenged, which could result in them being
narrowed in scope or declared invalid or unenforceable. There can be no assurance our intellectual property rights will be sufficient to protect against others offering products or services that are substantially similar to ours and compete with our
business.

We rely on non-patented proprietary information and technology, such as trade secrets, confidential information, know-how and
technical information. While in certain cases we have agreements in place with employees and third parties that place restrictions on the use and disclosure of this intellectual property, these agreements may be breached, or this intellectual
property may otherwise be disclosed or become known to our competitors, which could cause us to lose any competitive advantage resulting from this intellectual property.

We are pursuing registration of trademarks and domain names in the United States and in certain jurisdictions outside of the United States. Effective protection of trademarks and domain names is expensive and
difficult to maintain, both in terms of application and registration costs as well as the costs of defending and enforcing those rights. We may be required to protect our rights in an increasing number of countries, a process that is expensive and
may not be successful or which we may not pursue in every country in which our products and services are distributed or made available.

We are party to numerous agreements that grant licenses to third parties to use our intellectual property, including our trademarks. For example,
many third parties distribute their content through Twitter, or embed Twitter content in their applications or on their websites, and make use of our trademarks in connection with their services. If the licensees of our trademarks are not using our
trademarks properly, it may limit our ability to protect our trademarks and could ultimately result in our trademarks being declared invalid or unenforceable. We have a policy designed to assist third parties in the proper use of our brand,
trademarks and other assets, and we have an internal team dedicated to enforcing our policy and protecting our brand. Our brand protection team routinely receives and reviews reports of improper and unauthorized use of the Twitter brand, trademarks
or assets and issues takedown notices or initiates discussions with the third parties to correct the issues. However, there can be no assurance that we will be able to protect against the unauthorized use of our brand, trademarks or other assets. If
we fail to maintain and enforce our trademark rights, the value of our brand could be diminished. There is also a risk that one or more of our trademarks could become generic, which could result in them being declared invalid or unenforceable. For
example, there is a risk that the word Tweet could become so commonly used that it becomes synonymous with any short comment posted publicly on the Internet, and if this happens, we could lose protection of this trademark.

We also seek to obtain patent protection for some of our technology and as of June 30, 2013, we had 6 issued U.S. patents and approximately 80
patent applications on file in the United States and abroad, although there can be no assurance that these applications will be ultimately issued as patents. We may be unable to obtain patent or trademark protection for our technologies and brands,
and our existing patents and trademarks, and any patents or trademarks that may be issued in the future, may not provide us with competitive advantages or distinguish our products and services from those of our competitors. In addition, any patents
and trademarks may be contested, circumvented, or found unenforceable or invalid, and we may not be able to prevent third parties from infringing, diluting or otherwise violating them. Effective protection of patent rights is expensive and difficult
to maintain, both in terms of application and maintenance costs, as well as the costs of defending and enforcing those rights.

Our
Innovators Patent Agreement, or IPA, also limits our ability to prevent infringement of our patents. In May 2013, we implemented the IPA, which we enter into with our employees and consultants,

including our founders. The IPA, which applies to our current and future patents, allows us to assert our patents defensively. The IPA also allows us to assert our patents offensively with the
permission of the inventors of the applicable patent. Under the IPA, an assertion of claims is considered for a defensive purpose if the claims are asserted: (i) against an entity that has filed, maintained, threatened or voluntarily
participated in a patent infringement lawsuit against us or any of our users, affiliates, customers, suppliers or distributors; (ii) against an entity that has used its patents offensively against any other party in the past ten years, so long
as the entity has not instituted the patent infringement lawsuit defensively in response to a patent litigation threat against the entity; or (iii) otherwise to deter a patent litigation threat against us or our users, affiliates, customers,
suppliers or distributors. In addition, the IPA provides that the above limitations apply to any future owner or exclusive licensee of any of our patents, which could limit our ability to sell or license our patents to third parties. While we may be
able to claim protection of our intellectual property under other rights, such as trade secrets or contractual obligations with our employees not to disclose or use confidential information, we may be unable to assert our patent rights against third
parties that we believe are infringing our patents, even if such third parties are developing products and services that compete with our products and services. For example, in the event that an inventor of one of our patents leaves us for another
company and uses our patented technology to compete with us, we would not be able to assert that patent against such other company unless the assertion of the patent right is for a defensive purpose. In such event, we may be limited in our ability
to assert a patent right against another company, and instead would need to rely on trade secret protection or the contractual obligation of the inventor to us not to disclose or use our confidential information. In addition, the terms of the IPA
could affect our ability to monetize our intellectual property portfolio.

Significant impairments of our intellectual property rights,
and limitations on our ability to assert our intellectual property rights against others, could harm our business and our ability to compete. Also, obtaining, maintaining and enforcing our intellectual property rights is costly and time consuming.
Any increase in the unauthorized use of our intellectual property could make it more expensive to do business and harm our operating results.

We
are currently, and expect to be in the future, party to intellectual property rights claims that are expensive and time consuming to defend, and, if resolved adversely, could have a significant impact on our business, financial condition or
operating results.

Companies in the Internet, technology and media industries own large numbers of patents, copyrights,
trademarks and trade secrets, and frequently enter into litigation based on allegations of infringement, misappropriation or other violations of intellectual property or other rights. Many companies in these industries, including many of our
competitors, have substantially larger patent and intellectual property portfolios than we do, which could make us a target for litigation as we may not be able to assert counterclaims against parties that sue us for patent, or other intellectual
property infringement. In addition, various non-practicing entities that own patents and other intellectual property rights often attempt to aggressively assert claims in order to extract value from technology companies. Further, from
time to time we may introduce new products and services, including in areas where we currently do not have an offering, which could increase our exposure to patent and other intellectual property claims from competitors and non-practicing entities.
In addition, although our standard terms and conditions for our Promoted Products and public APIs do not provide advertisers and platform partners with indemnification for intellectual property claims against them, some of our agreements with
advertisers, platform partners and data partners require us to indemnify them for certain intellectual property claims against them, which could require us to incur considerable costs in defending such claims, and may require us to pay significant
damages in the event of an adverse ruling. Such advertisers, platform partners and data partners may also discontinue use of our products, services and technologies as a result of injunctions or otherwise, which could result in loss of revenue and
adversely impact our business.

We presently are involved in a number of intellectual property lawsuits, and as we face increasing
competition and gain an increasingly high profile, we expect the number of patent and other intellectual property claims against us to grow. There may be intellectual property or other rights held by others, including issued or pending patents, that
cover significant aspects of our products and services, and we cannot be sure that we are not infringing or violating, and have not infringed or violated, any third-party intellectual property rights or that we will not be held to have done so or be
accused of doing so in the future. Any claim or litigation alleging that we have infringed or otherwise violated intellectual property or other rights of third parties, with or without merit, and whether or not settled out of court or determined in
our favor, could be time-consuming and costly to address and resolve, and could divert the time and attention of our management and technical personnel. Some of our competitors have substantially greater resources than we do and are able to sustain
the costs of complex intellectual property litigation to a greater degree and for longer periods of time than we could. The outcome of any litigation is inherently uncertain, and there can be no assurances that favorable final outcomes will be
obtained in all cases. In addition, plaintiffs may seek, and we may become subject to, preliminary or provisional rulings in the course of any such litigation, including potential preliminary injunctions requiring us to cease some or all of our
operations. We may decide to settle such lawsuits and disputes on terms that are unfavorable to us. Similarly, if any litigation to which we are a party is resolved adversely, we may be subject to an unfavorable judgment that may not be reversed
upon appeal. The terms of such a settlement or judgment may require us to cease some or all of our operations or pay substantial amounts to the other party. In addition, we may have to seek a license to continue practices found to be in violation of
a third partys rights. If we are required, or choose to enter into royalty or licensing arrangements, such arrangements may not be available on reasonable terms, or at all, and may significantly increase our operating costs and expenses. As a
result, we may also be required to develop or procure alternative non-infringing technology or discontinue use of the technology. The development or procurement of alternative non-infringing technology could require significant effort and expense or
may not be feasible. An unfavorable resolution of the disputes and litigation referred to above could adversely affect our business, financial condition, and operating results.

Many of our products and services contain open source software, and we license some of our software through open source projects, which may pose particular risks to our proprietary software, products, and
services in a manner that could have a negative effect on our business.

We use open source software in our products and services
and will use open source software in the future. In addition, we regularly contribute software source code to open source projects under open source licenses or release internal software projects under open source licenses, and anticipate doing so
in the future. The terms of many open source licenses to which we are subject have not been interpreted by U.S. or foreign courts, and there is a risk that open source software licenses could be construed in a manner that imposes unanticipated
conditions or restrictions on our ability to provide or distribute our products or services. Additionally, we may from time to time face claims from third parties claiming ownership of, or demanding release of, the open source software or derivative
works that we developed using such software, which could include our proprietary source code, or otherwise seeking to enforce the terms of the applicable open source license. These claims could result in litigation and could require us to make our
software source code freely available, purchase a costly license or cease offering the implicated products or services unless and until we can re-engineer them to avoid infringement. This re-engineering process could require significant additional
research and development resources, and we may not be able to complete it successfully. In addition to risks related to license requirements, use of certain open source software can lead to greater risks than use of third-party commercial software,
as open source licensors generally do not provide warranties or controls on the origin of software. Additionally, because any software source code we contribute to open source projects is publicly available, our ability to protect our intellectual
property rights with respect to such software source code may be limited or lost entirely, and we are unable to prevent our competitors or

others from using such contributed software source code. Any of these risks could be difficult to eliminate or manage, and, if not addressed, could have a negative effect on our business,
financial condition and operating results.

We may expend substantial funds in connection with the tax liabilities that arise upon the initial
settlement of RSUs in connection with this offering, and the manner in which we fund that expenditure may have an adverse effect on our financial condition.

We may expend substantial funds to satisfy tax withholding and remittance obligations when we settle a portion of our RSUs granted prior to the date of this prospectus. Pre-2013 RSUs vest upon the satisfaction of
both a service condition and a performance condition. The service condition for the majority of the Pre-2013 RSUs is satisfied over a period of four years. The performance condition in connection with our Pre-2013 RSUs will be satisfied on the
earlier of (i) the date that is the earlier of (x) six months after the effective date of this offering or (y) March 8th of the calendar year following the effective date of this offering (which we may elect to accelerate to
February 15th); and (ii) the date of a change in control. On the settlement dates for the Pre-2013 RSUs, we may choose to allow our employees who are not executive officers to sell shares of our common stock received upon the vesting and
settlement of Pre-2013 RSUs in the public market to satisfy their income tax obligations related to the vesting and settlement of such awards, or we may withhold shares and remit income taxes on behalf of the holders of the Pre-2013 RSUs at the
applicable minimum statutory rates, which we refer to as a net settlement. We expect the applicable minimum statutory rates to be approximately 40% on average, and the income taxes due would be based on the then-current value of the underlying
shares of our common stock. Based on the number of Pre-2013 RSUs outstanding as of June 30, 2013 for which the service condition had been satisfied on that date, and assuming (i) the performance condition had been satisfied on that date and
(ii) that the price of our common stock at the time of settlement was equal to $ , which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, we
estimate that this tax obligation on the initial settlement date would be approximately $ in the aggregate. The amount of this obligation could be higher or lower, depending on the price of shares of
our common stock on the initial settlement date for the Pre-2013 RSUs. To settle these Pre-2013 RSUs on the initial settlement date, assuming a 40% tax withholding rate, if we choose to undertake a net settlement of all of these awards rather than
allowing our employees who are not executive officers to sell shares of our common stock in the public market to satisfy their income tax obligations related to the vesting and settlement of Pre-2013 RSUs, we would expect to deliver an aggregate of
approximately shares of our common stock to Pre-2013 RSU holders and withhold an aggregate of approximately
shares of our common stock. In connection with these net settlements, we would withhold and remit the tax liabilities on behalf of the Pre-2013 RSU holders to the relevant tax
authorities in cash.

If we choose to undertake a net settlement of our Pre-2013 RSUs, then in order to fund the tax withholding and
remittance obligations on behalf of our Pre-2013 RSU holders, we would expect to use a substantial portion of our cash and cash equivalent balances, or, alternatively, we may choose to borrow funds or a combination of cash and borrowed funds to
satisfy these obligations.

We may require additional capital to support our operations or the growth of our business, and we cannot be certain
that this capital will be available on reasonable terms when required, or at all.

From time to time, we may need additional
financing to operate or grow our business. Our ability to obtain additional financing, if and when required, will depend on investor and lender demand, our operating performance, the condition of the capital markets and other factors, and we cannot
assure you that additional financing will be available to us on favorable terms when required, or at all. If we raise additional funds through the issuance of equity, equity-linked or debt securities, those securities may have rights, preferences or
privileges senior to the rights of our common stock, and our existing stockholders may experience dilution. If we are unable to obtain adequate financing or financing on

terms satisfactory to us when we require it, our ability to continue to support the operation or growth of our business could be significantly impaired and our operating results may be harmed.

We rely on assumptions and estimates to calculate certain of our key metrics, and real or perceived inaccuracies in such metrics may harm our
reputation and negatively affect our business.

The numbers of our active users and timeline views are calculated using internal
company data that has not been independently verified. While these numbers are based on what we believe to be reasonable calculations for the applicable period of measurement, there are inherent challenges in measuring usage and user engagement
across our large user base around the world. For example, there are a number of false or spam accounts in existence on our platform. We currently estimate that false or spam accounts represent less than 5% of our MAUs. However, this estimate is
based on an internal review of a sample of accounts and we apply significant judgment in making this determination. As such, our estimation of false or spam accounts may not accurately represent the actual number of such accounts, and the actual
number of false or spam accounts could be higher than we have currently estimated. We are continually seeking to improve our ability to estimate the total number of spam accounts and eliminate them from the calculation of our active users, but we
otherwise treat multiple accounts held by a single person or organization as multiple users for purposes of calculating our active users because we permit people and organizations to have more than one account. Additionally, some accounts used by
organizations are used by many people within the organization. As such, the calculations of our active users may not accurately reflect the actual number of people or organizations using our platform.

Our metrics are also affected by mobile applications that automatically contact our servers for regular updates with no user action involved, and
this activity can cause our system to count the user associated with such a device as an active user on the day such contact occurs. The calculations of MAUs presented in this prospectus may be affected by this activity. The impact of this automatic
activity on our metrics varies by geography because mobile application usage varies in different regions of the world. In addition, our data regarding user geographic location is based on the IP address associated with the account when a user
initially registered the account on Twitter. The IP address may not always accurately reflect a users actual location at the time of user engagement on our platform.

We present and discuss timeline views in the six months ended June 30, 2012, but we did not track all of the timeline views on our mobile applications during the three months ended March 31, 2012. We have included
in this prospectus estimates for actual timeline views in the three months ended March 31, 2012 for the mobile applications we did not track. We believe these estimates to be reasonable, but actual numbers could differ from our estimates. In
addition, timeline views in the three months and six months ended June 30, 2012 exclude an immaterial number of timeline views in our mobile applications, certain of which were not fully tracked until June 2012.

We regularly review and may adjust our processes for calculating our internal metrics to improve their accuracy. Our measures of user growth and
user engagement may differ from estimates published by third parties or from similarly-titled metrics of our competitors due to differences in methodology. If advertisers, platform partners or investors do not perceive our user metrics to be
accurate representations of our user base or user engagement, or if we discover material inaccuracies in our user metrics, our reputation may be harmed and advertisers and platform partners may be less willing to allocate their budgets or resources
to our products and services, which could negatively affect our business and operating results.

We depend on highly skilled personnel to grow and
operate our business, and if we are unable to hire, retain and motivate our personnel, we may not be able to grow effectively.

managers. Our ability to execute efficiently is dependent upon contributions from our employees, in particular our senior management team. We do not have employment agreements other than offer
letters with any member of our senior management or other key employee, and we do not maintain key person life insurance for any employee. In addition, from time to time, there may be changes in our senior management team that may be disruptive to
our business. If our senior management team, including any new hires that we may make, fails to work together effectively and to execute our plans and strategies on a timely basis, our business could be harmed.

Our growth strategy also depends on our ability to expand and retain our organization with highly skilled personnel. Identifying, recruiting,
training and integrating qualified individuals will require significant time, expense and attention. In addition to hiring new employees, we must continue to focus on retaining our best employees. Many of our employees may be able to receive
significant proceeds from sales of our equity in the public markets after this offering, which may reduce their motivation to continue to work for us. Competition for highly skilled personnel is intense, particularly in the San Francisco Bay
Area, where our headquarters is located. We may need to invest significant amounts of cash and equity to attract and retain new employees and we may never realize returns on these investments. If we are not able to effectively add and retain
employees, our ability to achieve our strategic objectives will be adversely impacted, and our business will be harmed.

Our corporate culture has
contributed to our success, and if we cannot maintain this culture as we grow, we could lose the innovation, creativity and teamwork fostered by our culture, and our business may be harmed.

We believe that our culture has been and will continue to be a key contributor to our success. From January 1, 2010 to June 30, 2013, we
increased the size of our workforce by more than 1,800 employees, and we expect to continue to hire aggressively as we expand. If we do not continue to develop our corporate culture or maintain our core values as we grow and evolve, we may be unable
to foster the innovation, creativity and teamwork we believe we need to support our growth. Moreover, liquidity available to our employee securityholders following this offering could lead to disparities of wealth among our employees, which could
adversely impact relations among employees and our culture in general. Our transition from a private company to a public company may result in a change to our corporate culture, which could harm our business.

We rely in part on application marketplaces and Internet search engines to drive traffic to our products and services, and if we fail to appear high up in
the search results or rankings, traffic to our platform could decline and our business and operating results could be adversely affected.

We rely on application marketplaces, such as Apples App Store and Googles Play, to drive downloads of our mobile applications. In the future, Apple, Google or other operators of application marketplaces
may make changes to their marketplaces which make access to our products and services more difficult. We also depend in part on Internet search engines, such as Google, Bing and Yahoo!, to drive traffic to our website. For example, when a user types
an inquiry into a search engine, we rely on a high organic search result ranking of our webpages in these search results to refer the user to our website. However, our ability to maintain high organic search result rankings is not within our
control. Our competitors search engine optimization, or SEO, efforts may result in their websites receiving a higher search result page ranking than ours, or Internet search engines could revise their methodologies in a way that would
adversely affect our search result rankings. For example, Google has integrated its social networking offerings, including Google+, with certain of its products, including search, which has negatively impacted the organic search ranking of our
webpages. If Internet search engines modify their search algorithms in ways that are detrimental to us, or if our competitors SEO efforts are more successful than ours, the growth in our user base could slow. Our website has experienced
fluctuations in search result rankings in the past, and we anticipate similar fluctuations in

the future. Any reduction in the number of users directed to our mobile applications or website through application marketplaces and search engines could harm our business and operating results.

More people are using devices other than personal computers to access the Internet and new platforms to produce and consume content, and we need
to continue to promote the adoption of our mobile applications, and our business and operating results may be harmed if we are unable to do so.

The number of people who access the Internet through devices other than personal computers, including mobile phones, smartphones, handheld computers such as net books and tablets, video game consoles and television
set-top devices, has increased dramatically in the past few years. In the three months ended June 30, 2013, over 65% of our advertising revenue was generated from mobile devices. Since we generate a majority of our advertising revenue through users
on mobile devices, we must continue to drive adoption of our mobile applications. In addition, mobile users frequently change or upgrade their mobile devices. Our business and operating results may be harmed if our users do not install our mobile
application when they change or upgrade their mobile device. Although we generate the majority of our advertising revenue from ad engagements on mobile devices, certain of our products and services, including Promoted Trends and Promoted Accounts,
receive less prominence on our mobile applications than they do on our desktop applications. This has in the past reduced, and may in the future continue to reduce, the amount of revenue we are able to generate from these products and services as
users increasingly access our products and services through mobile and alternative devices. In addition, as new devices and platforms are continually being released, users may consume content in a manner that is more difficult to monetize. It is
difficult to predict the problems we may encounter in adapting our products and services and developing competitive new products and services that are compatible with new devices or platforms. If we are unable to develop products and services that
are compatible with new devices and platforms, or if we are unable to drive continued adoption of our mobile applications, our business and operating results may be harmed.

Future acquisitions and investments could disrupt our business and harm our financial condition and operating results.

Our success will depend, in part, on our ability to expand our products and services, and grow our business in response to changing technologies, user and advertiser demands, and competitive pressures. In some
circumstances, we may determine to do so through the acquisition of complementary businesses and technologies rather than through internal development, including, for example, our recent acquisitions of Vine Labs, Inc., a mobile application that
enables users to create and distribute videos that are up to six seconds in length, and Bluefin Labs, Inc., a social television analytics company that provides data products to brand advertisers, agencies and television networks. We also recently
entered into a definitive agreement to acquire MoPub, a mobile-focused advertising exchange. The identification of suitable acquisition candidates can be difficult, time-consuming and costly, and we may not be able to successfully complete
identified acquisitions. The risks we face in connection with acquisitions include:

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diversion of management time and focus from operating our business to addressing acquisition integration challenges;

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coordination of research and development and sales and marketing functions;

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retention of key employees from the acquired company;

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cultural challenges associated with integrating employees from the acquired company into our organization;

the need to implement or improve controls, procedures, and policies at a business that prior to the acquisition may have lacked effective controls, procedures
and policies;

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liability for activities of the acquired company before the acquisition, including intellectual property infringement claims, violations of laws, commercial
disputes, tax liabilities and other known and unknown liabilities;

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unanticipated write-offs or charges; and

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litigation or other claims in connection with the acquired company, including claims from terminated employees, users, former stockholders or other third
parties.

Our failure to address these risks or other problems encountered in connection with our past or future
acquisitions and investments could cause us to fail to realize the anticipated benefits of these acquisitions or investments, cause us to incur unanticipated liabilities, and harm our business generally. Future acquisitions could also result in
dilutive issuances of our equity securities, the incurrence of debt, contingent liabilities, amortization expenses, incremental operating expenses or the write-off of goodwill, any of which could harm our financial condition or operating results.

If we fail to maintain an effective system of disclosure controls and internal control over financial reporting, our ability to produce timely
and accurate financial statements or comply with applicable regulations could be impaired.

As a public company, we will be
subject to the reporting requirements of the Securities Exchange Act of 1934, as amended, or the Exchange Act, the Sarbanes-Oxley Act of 2002, or the Sarbanes-Oxley Act, and the rules and regulations of
the . We expect that the requirements of these rules and regulations will continue to increase our legal, accounting and financial
compliance costs, make some activities more difficult, time consuming and costly, and place significant strain on our personnel, systems and resources.

The Sarbanes-Oxley Act requires, among other things, that we maintain effective disclosure controls and procedures and internal control over financial reporting. We are continuing to develop and refine our
disclosure controls and other procedures that are designed to ensure that information required to be disclosed by us in the reports that we will file with the SEC is recorded, processed, summarized and reported within the time periods specified in
SEC rules and forms, and that information required to be disclosed in reports under the Exchange Act is accumulated and communicated to our principal executive and financial officers. We are also continuing to improve our internal control over
financial reporting. In order to maintain and improve the effectiveness of our disclosure controls and procedures and internal control over financial reporting, we have expended, and anticipate that we will continue to expend, significant resources,
including accounting-related costs and significant management oversight.

Our current controls and any new controls that we develop may
become inadequate because of changes in conditions in our business. Further, weaknesses in our disclosure controls or our internal control over financial reporting may be discovered in the future. Any failure to develop or maintain effective
controls, or any difficulties encountered in their implementation or improvement, could harm our operating results or cause us to fail to meet our reporting obligations and may result in a restatement of our financial statements for prior periods.
Any failure to implement and maintain effective internal control over financial reporting also could adversely affect the results of management evaluations and independent registered public accounting firm audits of our internal control over
financial reporting that we will eventually be required to include in our periodic reports that will be filed with the SEC. Ineffective disclosure controls and procedures and internal control over financial reporting could also cause investors to
lose confidence in our reported financial and other information, which would likely have a negative effect on the trading price of our common stock. In addition, if we are unable to continue to meet these requirements, we may not be able to remain
listed on the .

We are not currently required to comply with the SEC rules that implement Section 404 of the
Sarbanes-Oxley Act, and are therefore not required to make a formal assessment of the effectiveness of our internal control over financial reporting for that purpose. Upon becoming a public company, we will be required provide an annual management
report on the effectiveness of our internal control over financial reporting commencing with our second annual report on Form 10-K. Our independent registered public accounting firm is not required to audit the effectiveness of our internal control
over financial reporting until after we are no longer an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act. At such time, our independent registered public accounting firm may issue a
report that is adverse in the event it is not satisfied with the level at which our internal control over financial reporting is documented, designed or operating.

Any failure to maintain effective disclosure controls and internal control over financial reporting could have a material and adverse effect on our business and operating results, and cause a decline in the price
of our common stock.

We are an emerging growth company, and any decision on our part to comply only with certain reduced reporting and disclosure
requirements applicable to emerging growth companies could make our common stock less attractive to investors.

We are an
emerging growth company, and, for as long as we continue to be an emerging growth company, we may choose to take advantage of exemptions from various reporting requirements applicable to other public companies but not to emerging growth
companies, including, but not limited to, not being required to have our independent registered public accounting firm audit our internal control over financial reporting under Section 404 of the Sarbanes-Oxley Act, reduced disclosure
obligations regarding executive compensation in our periodic reports and proxy statements, and exemptions from the requirements of holding a nonbinding advisory vote on executive compensation and stockholder approval of any golden parachute payments
not previously approved. We could be an emerging growth company for up to five years following the completion of this offering. We will cease to be an emerging growth company upon the earliest of: (i) the end of the fiscal year following the
fifth anniversary of this offering, (ii) the first fiscal year after our annual gross revenue are $1.0 billion or more, (iii) the date on which we have, during the previous three-year period, issued more than $1.0 billion in
non-convertible debt securities or (iv) the end of any fiscal year in which the market value of our common stock held by non-affiliates exceeded $700 million as of the end of the second quarter of that fiscal year. We cannot predict if
investors will find our common stock less attractive if we choose to rely on these exemptions. If some investors find our common stock less attractive as a result of any choices to reduce future disclosure, there may be a less active trading market
for our common stock and the price of our common stock may be more volatile.

Under the JOBS Act, emerging growth companies can also
delay adopting new or revised accounting standards until such time as those standards apply to private companies. We have irrevocably elected not to avail ourselves of this accommodation allowing for delayed adoption of new or revised accounting
standards, and, therefore, we will be subject to the same new or revised accounting standards as other public companies that are not emerging growth companies.

If currency exchange rates fluctuate substantially in the future, our operating results, which are reported in U.S. dollars, could be adversely affected.

As we continue to expand our international operations, we will become more exposed to the effects of fluctuations in currency exchange rates. We
incur expenses for employee compensation and other operating expenses at our international locations in the local currency, and accept payment from advertisers or data partners in currencies other than the U.S. dollar. Since we conduct business in

currencies other than U.S. dollars but report our operating results in U.S. dollars, we face exposure to fluctuations in currency exchange rates. Consequently, exchange rate fluctuations between
the U.S. dollar and other currencies could have a material impact on our operating results.

Our business is subject to the risks of earthquakes,
fire, power outages, floods and other catastrophic events, and to interruption by man-made problems such as terrorism.

A
significant natural disaster, such as an earthquake, fire, flood or significant power outage could have a material adverse impact on our business, operating results, and financial condition. Our headquarters and certain of our co-located data center
facilities are located in the San Francisco Bay Area, a region known for seismic activity. Despite any precautions we may take, the occurrence of a natural disaster or other unanticipated problems at our data centers could result in lengthy
interruptions in our services. In addition, acts of terrorism and other geo-political unrest could cause disruptions in our business. All of the aforementioned risks may be further increased if our disaster recovery plans prove to be inadequate. We
have implemented a disaster recovery program, which allows us to move production to a back-up data center in the event of a catastrophe. Although this program is functional, we do not currently serve network traffic equally from each data center, so
if our primary data center shuts down, there will be a period of time that our products or services, or certain of our products or services, will remain inaccessible to our users or our users may experience severe issues accessing our products and
services.

We do not carry business interruption insurance sufficient to compensate us for the potentially significant losses, including
the potential harm to our business that may result from interruptions in our ability to provide our products and services.

We may have exposure
to greater than anticipated tax liabilities, which could adversely impact our operating results.

Our income tax obligations are
based in part on our corporate operating structure, including the manner in which we develop, value and use our intellectual property and the scope of our international operations. The tax laws applicable to our international business activities,
including the laws of the United States and other jurisdictions, are subject to interpretation. The taxing authorities of the jurisdictions in which we operate may challenge our methodologies for valuing developed technology (or other intangible
assets) or intercompany arrangements, which could increase our worldwide effective tax rate and harm our financial condition and operating results. We are subject to review and audit by U.S. federal and state and foreign tax authorities. Tax
authorities may disagree with certain positions we have taken and any adverse outcome of such a review or audit could have a negative effect on our financial position and operating results. In addition, our future income taxes could be adversely
affected by earnings being lower than anticipated in jurisdictions that have lower statutory tax rates and higher than anticipated in jurisdictions that have higher statutory tax rates, by changes in the valuation of our deferred tax assets and
liabilities, or by changes in tax laws, regulations or accounting principles. Tax expenses, or disputes with tax authorities, could adversely impact our operating results.

If our goodwill or intangible assets become impaired, we may be required to record a significant charge to earnings.

Under GAAP, we review our intangible assets for impairment when events or changes in circumstances indicate the carrying value may not be recoverable. Goodwill is required to be tested for impairment at least
annually. As of June 30, 2013, we had recorded a total of $178.2 million of goodwill and intangible assets related to our acquisitions. An adverse change in market conditions, particularly if such change has the effect of changing one of our
critical assumptions or estimates, could result in a

change to the estimation of fair value that could result in an impairment charge to our goodwill or intangible assets. Any such material charges may have a material negative impact on our
operating results.

Our ability to use our net operating loss carryforwards and certain other tax attributes may be limited.

As of December 31, 2012, we had U.S. federal net operating loss carryforwards of approximately $298.8 million and state net operating loss
carryforwards of approximately $216.7 million. Under Sections 382 and 383 of Internal Revenue Code of 1986, as amended, or the Code, if a corporation undergoes an ownership change, the corporations ability to use its pre-change net
operating loss carryforwards and other pre-change tax attributes, such as research tax credits, to offset its post-change income and taxes may be limited. In general, an ownership change occurs if there is a cumulative change in our
ownership by 5% shareholders that exceeds 50 percentage points over a rolling three-year period. Similar rules may apply under state tax laws. In the event that it is determined that we have in the past experienced an ownership change,
or if we experience one or more ownership changes as a result of this offering or future transactions in our stock, then we may be limited in our ability to use our net operating loss carryforwards and other tax assets to reduce taxes owed on the
net taxable income that we earn. Any such limitations on the ability to use our net operating loss carryforwards and other tax assets could adversely impact our business, financial condition and operating results.

Risks Related to Ownership of Our Common Stock and this Offering

Existing executive officers, directors and holders of 5% or more of our common stock will collectively beneficially own % of our common stock and continue to have substantial control
over us after this offering, which will limit your ability to influence the outcome of important transactions, including a change in control.

Our directors, executive officers and each of our stockholders who own greater than 5% of our outstanding common stock and their affiliates, in the aggregate, will beneficially own
approximately % of the outstanding shares of our common stock after this offering, based on the number of shares outstanding as of June 30, 2013. As a result, these stockholders, if acting together, will be able to influence
or control matters requiring approval by our stockholders, including the election of directors and the approval of mergers, acquisitions or other extraordinary transactions. They may also have interests that differ from yours and may vote in a way
with which you disagree and which may be adverse to your interests. This concentration of ownership may have the effect of delaying, preventing or deterring a change in control of our company, could deprive our stockholders of an opportunity to
receive a premium for their common stock as part of a sale of our company and might ultimately affect the market price of our common stock.

Anti-takeover provisions contained in our amended and restated certificate of incorporation and amended and restated bylaws, as well as provisions of
Delaware law, could impair a takeover attempt.

Our amended and restated certificate of incorporation, amended and restated
bylaws and Delaware law contain or will contain provisions which could have the effect of rendering more difficult, delaying, or preventing an acquisition deemed undesirable by our board of directors. Among other things, our amended and restated
certificate of incorporation and amended and restated bylaws will include provisions:

authorizing blank check preferred stock, which could be issued by our board of directors without stockholder approval and may contain voting,
liquidation, dividend and other rights superior to our common stock;

limiting the ability of our stockholders to call and bring business before special meetings;



requiring advance notice of stockholder proposals for business to be conducted at meetings of our stockholders and for nominations of candidates for election to
our board of directors; and



controlling the procedures for the conduct and scheduling of board of directors and stockholder meetings.

These provisions, alone or together, could delay or prevent hostile takeovers and changes in control or changes in our management.

As a Delaware corporation, we are also subject to provisions of Delaware law, including Section 203 of the Delaware General Corporation law,
which prevents certain stockholders holding more than 15% of our outstanding common stock from engaging in certain business combinations without approval of the holders of at least two-thirds of our outstanding common stock not held by such 15% or
greater stockholder.

Any provision of our amended and restated certificate of incorporation, amended and restated bylaws or Delaware
law that has the effect of delaying, preventing or deterring a change in control could limit the opportunity for our stockholders to receive a premium for their shares of our common stock, and could also affect the price that some investors are
willing to pay for our common stock.

An active trading market for our common stock may never develop or be sustained.

We intend to apply for the listing of our common stock on
the under the symbol TWTR. However, we cannot assure you that an active trading market for our common stock will develop on that exchange or
elsewhere or, if developed, that any market will be sustained. Accordingly, we cannot assure you of the likelihood that an active trading market for our common stock will develop or be maintained, the liquidity of any trading market, your ability to
sell your shares of our common stock when desired or the prices that you may obtain for your shares.

The market price of our common stock may be
volatile, and you could lose all or part of your investment.

Prior to this offering, there has been no public market for shares
of our common stock. The initial public offering price of our common stock will be determined through negotiation between us and the underwriters. This price will not necessarily reflect the price at which investors in the market will be willing to
buy and sell shares of our common stock following this offering. In addition, the market price of our common stock following this offering is likely to be highly volatile and could be subject to wide fluctuations in response to various factors, some
of which are beyond our control.

The market price of our common stock following this offering may fluctuate substantially and may be
higher or lower than the initial public offering price. The market price of our common stock following this offering will depend on a number of factors many of which are beyond our control and may not be related to our operating performance. These
fluctuations could cause you to lose all or part of your investment in our common stock since you might be unable to sell your shares at or above the price you paid in this offering. Factors that could cause fluctuations in the market price of our
common stock include the following:

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price and volume fluctuations in the overall stock market from time to time;



volatility in the market prices and trading volumes of technology stocks;

changes in operating performance and stock market valuations of other technology companies generally, or those in our industry in particular;



sales of shares of our common stock by us or our stockholders;



failure of securities analysts to maintain coverage of us, changes in financial estimates by securities analysts who follow our company, or our failure to meet
these estimates or the expectations of investors;



the financial projections we may provide to the public, any changes in those projections or our failure to meet those projections;

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announcements by us or our competitors of new products or services;

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the publics reaction to our press releases, other public announcements and filings with the SEC;

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rumors and market speculation involving us or other companies in our industry;

general economic conditions and slow or negative growth of our markets.

In addition, in the past, following periods of volatility in the overall market and the market price of a particular companys securities,
securities class action litigation has often been instituted against these companies. This litigation, if instituted against us, could result in substantial costs and a diversion of our managements attention and resources.

A total of , or %, of our outstanding shares of our common stock after this offering
will be restricted from immediate resale, but may be sold on a stock exchange in the near future. The large number of shares eligible for public sale or subject to rights requiring us to register them for public sale could depress the market price
of our common stock.

The market price of our common stock could decline as a result of sales of a large number of shares of our
common stock in the market after this offering, and the perception that these sales could occur may also depress the market price of our common stock. Based on shares of our capital stock outstanding as of June 30, 2013, we will
have shares of our common stock outstanding after this offering. Our executive officers, directors and the holders of substantially all of our capital stock and securities
convertible into or exchangeable for our capital stock have entered into market standoff agreements with us or will enter into lock-up agreements with the underwriters under which they have agreed or will agree, subject to specific exceptions, not
to sell any of our stock for 180 days following the date of this prospectus. As a result of these agreements and the provisions of our investors rights

agreement described further in the section titled Description of Capital StockRegistration Rights, and subject to the provisions of Rule 144 or Rule 701, shares of our common
stock will be available for sale in the public market as follows:



beginning on the date of this prospectus, all shares of our common stock sold in this
offering will be immediately available for sale in the public market;



beginning as early as February 15, 2014, up to an aggregate of shares of our common
stock that are held by our employees who are not executive officers may be eligible for sale in the public market in order to satisfy the income tax obligations of such employees resulting from the vesting and settlement of a portion of the
outstanding Pre-2013 RSUs (or up to an aggregate of shares of our common stock held by our employees who are not executive officers if we choose to undertake a net settlement
of all of these awards to satisfy a portion of such income tax obligations); and



beginning 181 days after the date of this prospectus, the remainder of the shares of our common stock will be eligible for sale in the public market from time to
time thereafter, subject in some cases to the volume and other restrictions of Rule 144, as described below.

Upon
completion of this offering, stockholders owning an aggregate of shares will be entitled, under contracts providing for registration rights, to require us to register shares of
our common stock owned by them for public sale in the United States. In addition, we intend to file a registration statement to register approximately shares reserved for future
issuance under our equity compensation plans. Upon effectiveness of that registration statement, subject to the satisfaction of applicable exercise periods and expiration of the market standoff agreements and lock-up agreements referred to above,
the shares of our common stock issued upon exercise of outstanding stock options or the vesting of RSUs will be available for immediate resale in the United States in the open market.

Sales of our common stock as restrictions end or pursuant to registration rights may make it more difficult for us to sell equity securities in the
future at a time and at a price that we deem appropriate. These sales also could cause the price of our common stock to fall and make it more difficult for you to sell shares of our common stock.

In making your investment decision, you should understand that we and the underwriters have not authorized any other party to provide you with information
concerning us or this offering.

You should carefully evaluate all of the information in this prospectus. We have in the past
received, and may continue to receive, a high degree of media coverage, including coverage that is not directly attributable to statements made by our officers and employees, that incorrectly reports on statements made by our officers or employees,
or that is misleading as a result of omitting information provided by us, our officers or employees. We and the underwriters have not authorized any other party to provide you with information concerning us or this offering.

We may invest or spend the proceeds of this offering in ways with which you may not agree or in ways which may not yield a return.

The net proceeds from the sale of our shares of our common stock by us in this offering may be used for general corporate purposes, including
working capital, operating expenses and capital expenditures. We anticipate making capital expenditures in 2013 of approximately $225 million to $275 million, and we may use a portion of the net proceeds to fund our anticipated capital expenditures.
We also may use a portion of the net proceeds to satisfy our anticipated tax withholding and remittance obligations related to the settlement of our outstanding RSUs. Additionally, we may use a portion of the net proceeds to acquire businesses,
products, services or technologies. However, we do not have

agreements or commitments for any specific material acquisitions at this time. Our management will have considerable discretion in the application of the net proceeds, and you will not have
the opportunity, as part of your investment decision, to assess whether the proceeds are being used appropriately. Until the net proceeds are used, they may be placed in investments that do not produce significant income or that may lose value.

Purchasers in this offering will experience immediate and substantial dilution in the book value of their investment.

The assumed initial public offering price of $ per share, which is the midpoint of the estimated
offering price range set forth on the cover page of this prospectus, is substantially higher than the net tangible book value per share of our outstanding common stock immediately after this offering. Therefore, if you purchase our common stock in
this offering, you will incur immediate dilution of $ in the net tangible book value per share from the price you paid. In addition, purchasers who bought shares from us in this offering will have
contributed % of the total consideration paid to us by our stockholders to purchase shares of our common stock, in exchange for acquiring approximately % of our outstanding shares of our capital stock as
of June 30, 2013 after giving effect to this offering. The vesting of RSUs and the exercise of outstanding stock options and a warrant will result in further dilution.

If securities or industry analysts do not publish or cease publishing research or reports about us, our business or our market, or if they change their recommendations regarding our common stock adversely,
the price of our common stock and trading volume could decline.

The trading market for our common stock will be influenced by
the research and reports that securities or industry analysts may publish about us, our business, our market or our competitors. If any of the analysts who may cover us change their recommendation regarding our common stock adversely, or provide
more favorable relative recommendations about our competitors, the price of our common stock would likely decline. If any analyst who may cover us were to cease coverage of our company or fail to regularly publish reports on us, we could lose
visibility in the financial markets, which in turn could cause the price of our common stock or trading volume to decline.

We do not expect to
declare any dividends in the foreseeable future.

We do not anticipate declaring any cash dividends to holders of our common
stock in the foreseeable future. Consequently, investors may need to rely on sales of their common stock after price appreciation, which may never occur, as the only way to realize any future gains on their investment. Investors seeking cash
dividends should not purchase our common stock.

Prior to this offering, there has been limited trading of our common stock at prices that may be
higher than what our common stock will trade at once it is listed.

Prior to this offering, our shares have not been listed on
any stock exchange or other public trading market, but there has been some trading of our securities in private trades. These trades were speculative, and the trading price of our securities in these trades was privately negotiated. We cannot assure
you that the price of our common stock will equal or exceed the price at which our securities have traded prior to this offering.

This prospectus contains forward-looking statements within the meaning of the federal securities laws, which statements involve substantial risks
and uncertainties. Forward-looking statements generally relate to future events or our future financial or operating performance. In some cases, you can identify forward-looking statements because they contain words such as may,
will, should, expects, plans, anticipates, could, intends, target, projects, contemplates, believes,
estimates, predicts, potential or continue or the negative of these words or other similar terms or expressions that concern our expectations, strategy, plans or intentions. Forward-looking statements
contained in this prospectus include, but are not limited to, statements about:



our ability to attract and retain users and increase the level of engagement of our users;



our ability to develop or acquire new products and services, improve our existing products and services and increase the value of our products and services;



our ability to attract advertisers to our platform and increase the amount that advertisers spend with us;

our ability to successfully acquire and integrate companies and assets; and



our ability to successfully enter new markets and manage our international expansion.

We caution you that the foregoing list may not contain all of the forward-looking statements made in this prospectus.

You should not rely upon forward-looking statements as predictions of future events. We have based the forward-looking statements contained in this
prospectus primarily on our current expectations and projections about future events and trends that we believe may affect our business, financial condition, results of operations and prospects. The outcome of the events described in these
forward-looking statements is subject to risks, uncertainties and other factors described in the section titled Risk Factors and elsewhere in this prospectus. Moreover, we operate in a very competitive and rapidly changing environment.
New risks and uncertainties emerge from time to time and it is not possible for us to predict all risks and uncertainties that could have an impact on the forward-looking statements contained in this prospectus. We cannot assure you that the
results, events and circumstances reflected in the forward-looking statements will be achieved or occur, and actual results, events or circumstances could differ materially from those described in the forward-looking statements.

The forward-looking statements made in this prospectus relate only to events as of the date on which the statements are made. We undertake no
obligation to update any forward-looking statements made in this prospectus to reflect events or circumstances after the date of this prospectus or to reflect new information or the occurrence of unanticipated events, except as required by law. We
may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements and you should not place undue reliance on our forward-looking statements. Our forward-looking statements do not reflect the potential impact
of any future acquisitions, mergers, dispositions, joint ventures or investments we may make.

This prospectus contains estimates and information concerning our industry, including market size and growth rates of the markets in which we
participate, that are based on industry publications and reports. This information involves a number of assumptions and limitations, and you are cautioned not to give undue weight to these estimates. We have not independently verified the accuracy
or completeness of the data contained in these industry publications and reports. The industry in which we operate is subject to a high degree of uncertainty and risk due to variety of factors, including those described in the Risk
Factors section. These and other factors could cause results to differ materially from those expressed in these publications and reports.

We review a number of metrics, including MAUs, timeline views, timeline views per MAU and advertising revenue per timeline view, to evaluate our business, measure our performance, identify trends affecting our
business, formulate business plans and make strategic decisions. See the section titled Managements Discussion and Analysis of Financial Condition and Results of OperationKey Metrics for a discussion of how we calculate MAUs,
timeline views, timeline views per MAU and advertising revenue per timeline view.

The numbers of active users and timeline views
presented in this prospectus are based on internal company data. While these numbers are based on what we believe to be reasonable estimates for the applicable period of measurement, there are inherent challenges in measuring usage and user
engagement across our large user base around the world. For example, there are a number of false or spam accounts in existence on our platform. We currently estimate that false or spam accounts represent less than 5% of our MAUs. However, this
estimate is based on an internal review of a sample of accounts and we apply significant judgment in making this determination. As such, our estimation of false or spam accounts may not accurately represent the actual number of such accounts, and
the actual number of false or spam accounts could be higher than we have currently estimated. We are continually seeking to improve our ability to estimate the total number of spam accounts and eliminate them from the calculation of our active
users. For example, we made an improvement in our spam detection capabilities in the second quarter of 2013 and suspended a large number of accounts. Spam accounts that we have identified are not included in the active user numbers presented in this
prospectus. We treat multiple accounts held by a single person or organization as multiple users for purposes of calculating our active users because we permit people and organizations to have more than one account. Additionally, some accounts used
by organizations are used by many people within the organization. As such, the calculations of our active users may not accurately reflect the actual number of people or organizations using our platform.

Our metrics are also affected by applications that automatically contact our servers for regular updates with no user action involved, and this
activity can cause our system to count the users associated with such applications as active users on the day or days such contact occurs. In the three months ended June 30, 2013, approximately seven percent of all active users used applications
that have the capability to automatically contact our servers for regular updates. As such, the calculations of MAUs presented in this prospectus may be affected as a result of automated activity. We expect that the percentage of active users that
use applications that have the capability to automatically contact our servers for regular updates will decline over time, particularly as usage of our mobile applications increases.

In addition, our data regarding user geographic location for purposes of reporting the geographic location of our MAUs is based on the IP address
associated with the account when a user initially registered the account on Twitter. The IP address may not always accurately reflect a users actual location at the time of user engagement on our platform.

We present and discuss timeline views in the six months ended June 30, 2012, but we did not track all of the timeline views on our mobile
applications during the three months ended March 31,

2012. We have included in this prospectus estimates for actual timeline views in the three months ended March 31, 2012 for the mobile applications we did not track. We believe these
estimates to be reasonable, but actual numbers could differ from our estimates. In addition, timeline views in the three months and six months ended June 30, 2012 exclude an immaterial number of timeline views for our mobile applications,
certain of which were not fully tracked until June 2012.

We regularly review and may adjust our processes for calculating our internal
metrics to improve their accuracy. Our measures of user growth and user engagement may differ from estimates published by third parties or from similarly-titled metrics of our competitors due to differences in methodology.

We estimate that the net proceeds to us from the sale of shares of our common stock in this offering will be approximately
$ , based upon the assumed initial public offering price of $ per share, which is the midpoint of the estimated offering price range set forth on the
cover page of this prospectus, and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us. If the underwriters option to purchase additional shares of our common stock from us is
exercised in full, we estimate that the net proceeds to us would be approximately $ , after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.

Each $1.00 increase or decrease in the assumed initial public offering price of $ per
share would increase or decrease the net proceeds that we receive from this offering by approximately $ , assuming that the number of shares offered by us, as set forth on the cover page of this
prospectus, remains the same and after deducting the estimated underwriting discounts and commissions payable by us. Similarly, each increase or decrease of one million in the number of shares of our common stock offered by us would increase or
decrease the net proceeds that we receive from this offering by approximately $ , assuming the assumed initial public offering price remains the same and after deducting the estimated underwriting
discounts and commissions payable by us.

The principal purposes of this offering are to increase our capitalization and financial
flexibility, create a public market for our common stock and enable access to the public equity markets for us and our stockholders.

We
intend to use the net proceeds from this offering for general corporate purposes, including working capital, operating expenses and capital expenditures. We anticipate making capital expenditures in 2013 of approximately $225 million to $275
million, and we may use a portion of the net proceeds to fund our anticipated capital expenditures. We also may use a portion of the net proceeds to satisfy our anticipated tax withholding and remittance obligations related to the settlement of
our outstanding Pre-2013 RSUs, or we may choose to allow our employees who are not executive officers holding such awards to sell shares of our common stock in the public market to satisfy their income tax obligations related to the vesting and
settlement of such awards. Based on the number of Pre-2013 RSUs outstanding as of June 30, 2013 for which the service condition had been satisfied on that date, and assuming (i) the performance condition had been satisfied on that date,
(ii) we choose to undertake a net settlement of all of our Pre-2013 RSUs and (iii) that the price of our common stock at the time of settlement was equal to $ , which is the midpoint of the
estimated offering price range set forth on the cover page of this prospectus, we estimate that this tax obligation on the initial settlement date would be approximately $ in the aggregate. The amount
of this obligation could be higher or lower, depending on the price of shares of our common stock on the initial settlement date for the Pre-2013 RSUs. Additionally, we may use a portion of the net proceeds to acquire businesses, products, services
or technologies. However, except for our proposed acquisition of MoPub in exchange for shares of our common stock, we do not have agreements or commitments for any material acquisitions at this time. We cannot specify with certainty the
particular uses of the net proceeds that we will receive from this offering. Accordingly, we will have broad discretion in using these proceeds. Pending the use of proceeds from this offering as described above, we plan to invest the net proceeds
that we receive in this offering in short-term and long-term interest-bearing obligations, including government and investment-grade debt securities and money market funds.

DIVIDEND POLICY

We have never declared or paid any cash dividends
on our capital stock. We currently intend to retain any future earnings and do not expect to pay any dividends in the foreseeable future. Any future determination to declare cash dividends will be made at the discretion of our board of directors,
subject to applicable laws, and will depend on a number of factors, including our financial condition, results of operations, capital requirements, contractual restrictions, general business conditions and other factors that our board of directors
may deem relevant.

The following table sets forth cash and cash equivalents, as well as our capitalization, as of June 30, 2013 as follows:

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on an actual basis;

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on a pro forma basis, giving effect to (i) the automatic conversion of all outstanding shares of our Class A junior preferred stock and our convertible
preferred stock into an aggregate of 333,099,000 shares of our common stock, which conversion will occur immediately prior to the completion of this offering, as if such conversion had occurred on June 30, 2013, (ii) the resulting
reclassification of the restricted Class A junior preferred stock of $6.7 million and preferred stock warrant liability of $2.0 million from other long-term liabilities to additional paid-in capital, (iii) stock-based compensation expense
of $329.6 million associated with Pre-2013 RSUs for which the service condition was satisfied as of June 30, 2013, and which we expect to record upon completion of this offering, as described in footnote (1) below and (iv) the filing and
effectiveness of our amended and restated certificate of incorporation in Delaware; and

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on a pro forma as adjusted basis, giving effect to the pro forma adjustments set forth above and the sale and issuance by us of
shares of our common stock in this offering, based upon the assumed initial public offering price of $ per share, which is the midpoint of the estimated
offering price range set forth on the cover page of this prospectus, and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.

You should read this table together with our consolidated financial statements and related notes, and the sections titled Selected
Consolidated Financial and Other Data and Managements Discussion and Analysis of Financial Condition and Results of Operations that are included elsewhere in this prospectus.

As of June 30, 2013

Actual

ProForma(1)

Pro
FormaasAdjusted(2)

(In thousands, except share andper share data)

Cash, cash equivalents and short-term investments

$

375,058

$

375,058

$

Restricted Class A junior preferred stock and preferred stock warrant liabilities included in other long term
liabilities

The pro forma data as of June 30, 2013 gives effect to stock-based compensation
expense of $329.6 million associated with Pre-2013 RSUs for which the service condition was satisfied as of June 30, 2013 and which we expect to record upon completion of this offering, as further described in Managements Discussion and
Analysis of Financial Condition and Results of OperationsCritical Accounting Policies and EstimatesStock-Based Compensation. The pro forma adjustment related to stock-based compensation expense of $329.6 million has been reflected
as an increase to additional paid-in capital and accumulated deficit. We estimate that an aggregate of approximately million shares underlying
Pre-2013 RSUs outstanding as of June 30, 2013 will vest and settle on in connection with the satisfaction of the performance
condition to their vesting, resulting in the net issuance of an aggregate of approximately million shares to the holders if we choose to undertake
a net settlement of all of these awards rather than allowing our employees who are not executive officers to sell shares of our common stock in the public market to satisfy their income tax obligations related to the vesting and settlement of such
awards. These shares have not been included in our pro forma or pro forma as adjusted shares outstanding.

(2)

Each $1.00 increase or decrease in the assumed initial public offering price of our
common stock of $ per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, would increase or decrease, as applicable, the amount of our pro
forma as adjusted cash and cash equivalents, additional paid-in capital and total stockholders equity by approximately $ , assuming that the number of shares offered by us, as set forth on the
cover page of this prospectus, remains the same and after deducting estimated underwriting discounts and commissions payable by us. An increase or decrease of 1.0 million shares in the number of shares offered by us would increase or decrease,
as applicable, the amount of our pro forma as adjusted cash and cash equivalents, additional paid-in capital and total stockholders equity by approximately $ , assuming that the number of shares
offered by us, as set forth on the cover page of this prospectus, remains the same and after deducting estimated underwriting discounts and commissions payable by us.

If the underwriters option to purchase additional shares of our common stock from us were exercised in full, pro forma as adjusted cash and
cash equivalents, additional paid-in capital, total stockholders equity and shares outstanding as of June 30, 2013 would be $ , $ ,
$ and $ , respectively.

The pro forma
and pro forma as adjusted columns in the table above are based on 472,613,753 shares of our common stock (including preferred stock on an as-converted basis) outstanding as of June 30, 2013, and exclude the following:

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44,157,061 shares of our common stock issuable upon the exercise of options to purchase shares of our common stock outstanding as of June 30, 2013, with a
weighted-average exercise price of $1.82 per share;

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59,913,992 shares of our common stock subject to RSUs outstanding as of June 30, 2013;

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116,512 shares of our common stock, on an as-converted basis, issuable upon the exercise of a warrant to purchase convertible preferred stock outstanding as of
June 30, 2013, with an exercise price of $0.34 per share;

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27,002,040 shares of our common stock subject to RSUs granted after June 30, 2013;

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up to 14,791,464 shares of our common stock issuable upon completion of our acquisition of MoPub; and

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shares of our common stock reserved for future issuance under our equity compensation
plans which will become effective prior to the completion of this offering, consisting of:

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shares of our common stock reserved for future issuance under our 2013 Plan;



7,814,902 shares of our common stock reserved for future issuance under our 2007 Plan (after giving effect to an increase of 20,000,000 shares of our common
stock reserved for issuance under our 2007 Plan after June 30, 2013 and the grant of 27,002,040 shares of our common stock subject to RSUs granted after June 30, 2013), which number of shares will be added to the shares of our common stock to
be reserved under our 2013 Plan upon its effectiveness; and



shares of our common stock reserved for future issuance under our ESPP.

Our 2013 Plan and ESPP each provide for annual automatic increases in the number of shares reserved thereunder, and
our 2013 Plan also provides for increases to the number of shares that may be granted thereunder based on shares under our 2007 Plan that expire, are forfeited or otherwise repurchased by us, as more fully described in the section titled
Executive CompensationEmployee Benefit and Stock Plans.

If you invest in our common stock in this offering, your ownership interest will be diluted to the extent of the difference between the initial
public offering price per share of our common stock and the pro forma as adjusted net tangible book value per share of our common stock immediately after this offering. Net tangible book value dilution per share to new investors represents the
difference between the amount per share paid by purchasers of shares of our common stock in this offering and the pro forma as adjusted net tangible book value per share of our common stock immediately after completion of this offering.

Net tangible book value per share is determined by dividing our total tangible assets less our total liabilities by the number of shares of our
common stock outstanding. Our historical net tangible deficit as of June 30, 2013 was $342.5 million, or $2.46 per share. Our pro forma net tangible book value as of June 30, 2013 was $538.7 million, or $1.14 per share, based on the total
number of shares of our common stock outstanding as of June 30, 2013, after giving effect to the automatic conversion of all outstanding shares of our Class A junior preferred stock and our convertible preferred stock as of June 30, 2013 into
an aggregate of 333,099,000 shares of our common stock, which conversion will occur immediately prior to the completion of this offering, and the resulting reclassification of the restricted Class A junior preferred stock and preferred stock
warrant liability from other long-term liabilities to additional paid-in capital.

After giving effect to the sale by us of
shares of our common stock in this offering at the assumed initial public offering price of $ per share, which is the midpoint
of the estimated offering price range set forth on the cover page of this prospectus, and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us, our pro forma as adjusted net tangible book
value as of June 30, 2013 would have been $ million, or $ per share. This represents an immediate increase in pro forma net tangible book value of
$ per share to our existing stockholders and an immediate dilution in pro forma net tangible book value of $ per share to investors purchasing shares of
our common stock in this offering at the assumed initial public offering price. The following table illustrates this dilution:

Assumed initial public offering price per share

$

Pro forma net tangible book value (deficit) per share as of June 30, 2013

$

1.14

Increase in pro forma net tangible book value (deficit) per share attributable to new investors in this offering

Pro forma as adjusted net tangible book value per share immediately after this offering

Dilution in pro forma net tangible book value per share to new investors in this offering

$

Each $1.00 increase or decrease in the assumed initial public offering price of
$ per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, would increase or decrease, as applicable, our pro forma as adjusted net
tangible book value per share to new investors by $ , and would increase or decrease, as applicable, dilution per share to new investors in this offering by
$ , assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same and after deducting estimated underwriting discounts and commissions and
estimated offering expenses payable by us. Similarly, each increase or decrease of 1.0 million shares in the number of shares offered by us would increase or decrease, as applicable, our pro forma as adjusted net tangible book value by
approximately $ per share and increase or decrease, as applicable, the dilution to new investors by $ per share, assuming the assumed initial public
offering price remains the same, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us.

If the underwriters option to purchase additional shares of our common stock from us is
exercised in full, the pro forma as adjusted net tangible book value per share of our common stock, as adjusted to give effect to this offering, would be $ per share, and the dilution in pro forma net
tangible book value per share to new investors in this offering would be $ per share.

The following table presents, as of June 30, 2013, after giving effect to the automatic conversion of all outstanding shares of our Class A
junior preferred stock and our convertible preferred stock into our common stock immediately prior to the completion of this offering, the differences between the existing stockholders and the new investors purchasing shares of our common stock in
this offering with respect to the number of shares purchased from us, the total consideration paid or to be paid to us, which includes net proceeds received from the issuance of our common stock and preferred stock, cash received from the exercise
of stock options and the average price per share paid or to be paid to us at the assumed initial public offering price of $ per share, which is the midpoint of the estimated offering price range set
forth on the cover page of this prospectus, before deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us:

Shares Purchased

Total Consideration

AveragePrice PerShare

Number

Percent

Amount

Percent

Existing stockholders

%

$

%

$

New investors

Totals

100

%

$

100

%

Each $1.00 increase or decrease in the assumed initial public offering price of
$ per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, would increase or decrease, as applicable, the total consideration paid by new
investors and total consideration paid by all stockholders by approximately $ , assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same and
after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.

Except as otherwise
indicated, the above discussion and tables assume no exercise of the underwriters option to purchase additional shares of our common stock from us. If the underwriters option to purchase additional shares of our common stock were
exercised in full, our existing stockholders would own % and our new investors would own % of the total number of shares of our common stock outstanding upon the completion of this offering.

The number of shares of our common stock that will be outstanding after this offering is based on 472,613,753 shares of our common
stock (including preferred stock on an as-converted basis) outstanding as of June 30, 2013, and excludes:



44,157,061 shares of our common stock issuable upon the exercise of options to purchase shares of our common stock outstanding as of June 30, 2013, with a
weighted-average exercise price of $1.82 per share;



59,913,992 shares of our common stock subject to RSUs outstanding as of June 30, 2013;



116,512 shares of our common stock, on an as-converted basis, issuable upon the exercise of a warrant to purchase convertible preferred stock outstanding as of
June 30, 2013, with an exercise price of $0.34 per share;



27,002,040 shares of our common stock subject to RSUs granted after June 30, 2013;



up to 14,791,464 shares of our common stock issuable upon completion of our acquisition of MoPub; and

shares of our common stock reserved for future issuance under our equity compensation
plans which will become effective prior to the completion of this offering, consisting of:



shares of our common stock reserved for future issuance under our 2013 Plan;



7,814,902 shares of our common stock reserved for future issuance under our 2007 Plan (after giving effect to an increase of 20,000,000 shares of our common
stock reserved for issuance under our 2007 Plan after June 30, 2013 and the grant of 27,002,040 shares of our common stock subject to RSUs granted after June 30, 2013), which number of shares will be added to the shares of our common stock to
be reserved under our 2013 Plan upon its effectiveness; and



shares of our common stock reserved for future issuance under our ESPP.

Our 2013 Plan and ESPP each provide for annual automatic increases in the number of shares reserved thereunder, and
our 2013 Plan also provides for increases to the number of shares that may be granted thereunder based on shares under our 2007 Plan that expire, are forfeited or otherwise repurchased by us, as more fully described in the section titled
Executive CompensationEmployee Benefit and Stock Plans.

To the extent that any outstanding options to purchase our
common stock or a warrant to purchase convertible preferred stock are exercised, RSUs are settled or new awards are granted under our equity compensation plans, there will be further dilution to investors participating in this offering.

The following selected consolidated statement of operations data for the years ended December 31, 2010, 2011 and 2012 and the consolidated
balance sheet data as of December 31, 2011 and 2012 have been derived from our audited consolidated financial statements included elsewhere in this prospectus. The consolidated balance sheet data as of December 31, 2010 has been derived
from our audited consolidated financial statements not included in this prospectus. The selected consolidated statement of operations data for the six months ended June 30, 2012 and 2013 and the consolidated balance sheet data as of June 30, 2013
have been derived from our unaudited interim consolidated financial statements included elsewhere in this prospectus. The unaudited interim consolidated financial statements have been prepared on the same basis as the audited financial statements
and reflect, in the opinion of management, all adjustments, of a normal, recurring nature that are necessary for a fair statement of the unaudited interim consolidated financial statements. Our historical results are not necessarily indicative of
the results that may be expected in the future and the results in the six months ended June 30, 2013 are not necessarily indicative of results to be expected for the full year or any other period. You should read the following selected consolidated
financial and other data below in conjunction with the section titled Managements Discussion and Analysis of Financial Condition and Results of Operations and our consolidated financial statements and related notes included
elsewhere in this prospectus.

Year Ended December 31,

Six Months EndedJune 30,

2010

2011

2012

2012

2013

(In thousands, except per share data)

Consolidated Statement of Operations Data:

Revenue

$

28,278

$

106,313

$

316,933

$

122,359

$

253,635

Costs and expenses(1)

Cost of revenue

43,168

61,803

128,768

58,157

91,828

Research and development

29,348

80,176

119,004

46,345

111,837

Sales and marketing

6,289

25,988

86,551

34,105

77,697

General and administrative

16,952

65,757

59,693

30,758

35,096

Total costs and expenses

95,757

233,724

394,016

169,365

316,458

Loss from operations

(67,479

)

(127,411

)

(77,083

)

(47,006

)

(62,823

)

Interest income (expense), net

55

(805

)

(2,486

)

(890

)

(2,746

)

Other income (expense), net

(117

)

(1,530

)

399

(12

)

(2,548

)

Loss before income taxes

(67,541

)

(129,746

)

(79,170

)

(47,908

)

(68,117

)

Provision (benefit) for income taxes

(217

)

(1,444

)

229

1,196

1,134

Net loss

$

(67,324

)

$

(128,302

)

$

(79,399

)

$

(49,104

)

$

(69,251

)

Deemed dividend to investors in relation to the tender offer



35,816







Net loss attributable to common stockholders

$

(67,324

)

$

(164,118

)

$

(79,399

)

$

(49,104

)

$

(69,251

)

Weighted-average shares used to compute net loss per share attributable to common stockholders:

Costs and expenses include stock-based compensation expense as follows:

Year Ended December 31,

Six Months EndedJune 30,

2010

2011

2012

2012

2013

(In thousands)

(Unaudited)

Cost of revenue

$

200

$

1,820

$

800

$

420

$

1,955

Research and development

3,409

33,559

12,622

6,291

24,197

Sales and marketing

249

1,553

1,346

620

4,614

General and administrative

2,073

23,452

10,973

8,796

4,802

Total stock-based compensation

$

5,931

$

60,384

$

25,741

$

16,127

$

35,568

(2)

See Note 9 to our consolidated financial statements for an explanation of the calculations of our pro forma net loss per share attributable to common
stockholders.

(3)

See the sections titled Prospectus SummarySummary Consolidated Financial and Other DataNon-GAAP Financial Measures for additional
information and a reconciliation of net loss to Adjusted EBITDA and net loss to non-GAAP net loss.

MANAGEMENTS DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND
RESULTS OF OPERATIONS

The following discussion and analysis of our financial condition and results of operations should be read
in conjunction with the section titled Selected Consolidated Financial and Other Data and the consolidated financial statements and related notes thereto included elsewhere in this prospectus. This discussion contains forward-looking
statements that involve risks and uncertainties. Our actual results could differ materially from those discussed below. Factors that could cause or contribute to such differences include, but are not limited to, those identified below and those
discussed in the section titled Risk Factors included elsewhere in this prospectus.

Overview

Twitter is a global platform for public self-expression and conversation in real time. Our platform is unique in its simplicity: Tweets are limited
to 140 characters of text. This constraint makes it easy for anyone to quickly create, distribute and discover content that is consistent across our platform and optimized for mobile devices. As a result, Tweets drive a high velocity of information
exchange that makes Twitter uniquely live.

We have already achieved significant global scale, and we continue to grow. We
have more than 215 million MAUs spanning nearly every country. Our users include millions of people from around the world, as well as influential individuals and organizations, such as world leaders, government officials, celebrities, athletes,
journalists, sports teams, media outlets and brands. Our users create approximately 500 million Tweets every day.

The value we
create for our users is enhanced by our platform partners and advertisers. Millions of platform partners, which include publishers, media outlets and developers, have integrated with Twitter, adding value to our user experience by contributing
content to our platform, broadly distributing content from our platform across their properties and using Twitter content and tools to enhance their websites and applications. In addition, advertisers use our Promoted Products to promote their
brands, products and services, amplify their visibility and reach, and complement and extend the conversation around their advertising campaigns. Although we do not generate revenue directly from users or platform partners, we benefit from network
effects where more activity on Twitter results in the creation and distribution of more content, which attracts more users, platform partners and advertisers, resulting in a virtuous cycle of value creation.

We generate the substantial majority of our revenue from the sale of advertising services, with the balance coming from data licensing
arrangements. We generate nearly all of our advertising revenue through the sale of our three Promoted Products: Promoted Tweets, Promoted Accounts and Promoted Trends. The substantial majority of our advertising revenue is generated on a
pay-for-performance basis, which means advertisers are only charged when a user engages with their ad, creating an attractive value proposition for our advertisers.

We launched our first Promoted Products in mid-2010 in the United States by introducing Promoted Tweets in search results and Promoted Trends. Since that time, we have expanded our Promoted Products to add Promoted
Accounts and extended our Promoted Products across our platform and to additional geographies. We generate advertising sales in the United States and certain other geographies through our direct sales force, as well as through our self-serve
advertising platform.

We introduced Promoted Products on our iOS and Android mobile applications in February 2012. Over 65% of our
advertising revenue was generated from mobile devices in the three months ended June 30, 2013.

Our international revenue was $53.0 million and $62.8 million in 2012 and the six months
ended June 30, 2013, respectively, representing 17% and 25% of our total revenue for those periods, respectively. We launched Promoted Products in selected international markets in the third quarter of 2011, and we expect to continue to launch our
Promoted Products in additional markets over time. We have recently focused our international spending on sales support and marketing activities in specific countries, including Australia, Brazil, Canada, Japan and the United Kingdom. In certain
international geographies where we have not invested to build a local sales force, we rely on resellers that serve as outside sales agents for the sale of our Promoted Products. In the six months ended June 30, 2013, we and our resellers sold our
Promoted Products to advertisers in over 20 countries outside of the United States. We record advertising revenue based on the billing location of our advertisers, rather than the location of our users.

We are headquartered in San Francisco, California, and have offices in over 15 cities around the world.

Key Milestones

We have developed our
advertising services through the introduction of numerous products and services, including:

We review a number of metrics, including the following key metrics, to evaluate our business, measure our performance, identify trends affecting our business, formulate business plans and make strategic decisions:

Monthly Active Users (MAUs). We define MAUs as Twitter users who logged in and accessed Twitter through
our website, mobile website, desktop or mobile applications, SMS or registered third-party applications or websites in the 30-day period ending on the date of measurement. Average MAUs for a period represent the average of the MAUs at the end of
each month during the period. In the discussion of our results of operations we compare average MAUs for the last three months of each period discussed in such comparison. MAUs are a measure of the size of our active user base. In the three months
ended June 30, 2013, we had 218.3 million average MAUs, which represents an increase of 44% from the three months ended June 30, 2012. In the three months ended June 30, 2013, we had 49.2 million average MAUs in the United States and
169.1 million average MAUs in the rest of the world, which represent increases of 35% and 47%, respectively, from the three months ended June 30, 2012. For additional information on how we calculate the number of MAUs and factors that can
affect this metric, see the section titled Industry Data and Company Metrics.

Timeline Views, Timeline Views Per MAUand Advertising Revenue Per Timeline
View. We define timeline views as the total number of timelines requested when registered users visit Twitter, refresh a timeline or view search results while logged in on our website, mobile website or desktop or mobile
applications (excluding our TweetDeck and Mac clients, as we do not fully track this data). We believe that timeline views and timeline views per MAU are measures of user engagement. Timeline views per MAU are calculated by dividing the total
timeline views for the period by the average MAUs for the last three months of such period. In the three months and six months ended June 30, 2013, we had 150.9 billion and 287.2 billion timeline views, respectively, which represent increases of 69%
and 79% from the three months and six months ended June 30, 2012, respectively. In the three months and six months ended June 30, 2013, we had 40.6 billion and 80.2 billion timeline views in the United States, respectively, which represent
increases of 45% and 57% from the three months and six months ended June 30, 2012, respectively. In the three months and six months ended June 30, 2013, we had 110.3 billion and 207.1 billion timeline views in the rest of the world,
respectively, which represent increases of 79% and 89% from the three months and six months ended June 30, 2012, respectively. In the three months ended June 30, 2013, we had 691 timeline views per MAU, which represents an increase of 17% from the
three months ended June 30, 2012. In the three months ended June 30, 2013, we had 825 timeline views per MAU in the United States and 652 timeline views per MAU in the rest of the world, which represent increases of 8% and 22% from the three months
ended June 30, 2012, respectively. For additional information on how we calculate the number of timeline views and factors that can affect this metric, see the section titled Industry Data and Company Metrics.

We define advertising revenue per timeline view as advertising revenue per 1,000 timeline views during the applicable period. We believe
that advertising revenue per timeline view is a measure of our ability to monetize our platform. In the three months ended June 30, 2013, our advertising revenue per timeline view was $0.80, which represents a 26% increase from the three months
ended June 30, 2012. In the three months ended June 30, 2013, our advertising revenue per timeline view in the United States was $2.17 and our advertising revenue per timeline view in the rest of the world was $0.30, which represent
increases of 26% and 111% from the three months ended June 30, 2012, respectively. We record advertising revenue based on the billing location of our advertisers, rather than the location of our users.

User Growth, User Engagement and Monetization. User growth trends reflected in the number of MAUs, user engagement trends reflected in timeline views and timeline views per MAU and
monetization trends reflected in advertising revenue per timeline view are key factors that affect our revenue. As our user base and the level of engagement of our users grow, we believe the potential to increase our revenue grows.

User Growth. We have experienced significant growth in our number of users over the last several
years. In general, a higher proportion of Internet users in the United States uses Twitter than Internet users in other countries. Accordingly, in the future we expect our user growth rate in certain international markets, such as Argentina, France,
Japan, Russia, Saudi Arabia and South Africa, to continue to be higher than our user growth rate in the United States. However, we expect to face challenges in entering some markets, such as China, where access to Twitter is blocked, as well as
certain other countries that have intermittently restricted access to Twitter. Restrictions or

limitations on access to Twitter may adversely impact our ability to increase the size of our user base and generate additional revenue in certain markets.

Our user base continues to grow. Although we do not separately track whether an MAU has only used Twitter on a desktop or on a
mobile device, the usage of our mobile applications continues to grow. In the three months ended June 30, 2013, 75% of our average MAUs accessed Twitter from a mobile device, compared to 66% in the three months ended June 30, 2012.

We may face challenges in increasing the size of our user base, including, among others, competition from alternative products and
services, a decline in the number of influential users on Twitter or a perceived decline in the quality of content available on Twitter. We intend to drive growth in our user base by continuing to demonstrate the value and usefulness of our products
and services to potential new users, and by introducing new products, services and features. We anticipate that our user growth rate will slow over time as the size of our user base increases. To the extent our user growth or user growth rate slows,
our revenue growth will become increasingly dependent on our ability to increase levels of user engagement, as measured by timeline views and timeline views per MAU, and monetization, as measured by advertising revenue per timeline view.

User Engagement. We broadly measure user engagement on our platform through timeline views and the
number of timeline views per MAU. In the three months ended June 30, 2013, timeline views increased 69% and timeline views per MAU increased 17%, compared to the three months ended June 30, 2012. We continue to develop products for our
platform, and to develop partnerships globally to increase relevant local content on our platform, with the goal of increasing our user engagement. In particular, our most engaged users are generally those who access Twitter via our mobile
applications. In the three months ended June 30, 2013, a substantial majority of timeline views were on mobile devices, and the increase in timeline views was driven by mobile user engagement. We expect this trend to continue in the near term, and
we plan to continue to develop and improve our mobile applications to further drive user adoption of these applications. However, to the extent user engagement as measured by timeline views and timeline views per MAU does not increase, our revenue
growth will depend in large part on our ability to increase MAUs or monetization of our platform.

Monetization. We measure monetization of our platform through advertising revenue per timeline view.
There are many variables that impact timeline views and advertising revenue per timeline view, such as the number of MAUs, the number of timeline views per MAU, which timeline views we monetize and the amount of advertising we choose to display, our
users engagement with our Promoted Products and advertiser demand. Generally, for our pay-for-performance Promoted Products, we design our algorithms to optimize for the combined impact of a number of factors, including the overall user
experience, the number of ads we deliver to a particular user, the likelihood that our users will engage with the ads, the value we deliver to advertisers and the impact of the advertisers bids. We design our algorithms to enhance the user
experience by delivering relevant ads to a user based on the users Interest Graph, and these ads may contain information of interest to the user or may provide promotional offers that are not available anywhere else. Our algorithms also
enhance the value that we deliver to advertisers because the targeting capabilities of our algorithms allow advertisers to deliver ads that are relevant to a users interests, thereby increasing the effectiveness of an advertisers
advertising campaign.

We regularly refine our algorithms to drive monetization while maximizing the long-term value of
our platform for our users and advertisers. Given the large number of variables that drive advertising revenue per timeline view, including decisions that we make regarding optimizing user experience and satisfying advertiser demand, certain
individual components may decline while others increase. Ultimately, it is the combination of the changes in these components that impacts advertising revenue per timeline view. For example, advertising revenue has increased sequentially in each of
the five quarters ended June 30, 2013, driven by sequential increases in paid user

engagements with our pay-for-performance Promoted Products, or ad engagements, over those same periods, partially offset by sequential decreases in average cost per ad engagement during the same
periods. The number of ad engagements increased 55%, 32%, 78%, 15% and 124% sequentially in the three months ended June 30, 2012, September 30, 2012, December 31, 2012, March 31, 2013 and June 30, 2013, respectively. The increases in ad engagements
over these periods were primarily due to increases in MAUs, user engagement levels, as measured by timeline views per MAU, and advertiser demand. Average cost per ad engagement decreased 18%, 9%, 19%, 12% and 46% sequentially in the three months
ended June 30, 2012, September 30, 2012, December 31, 2012, March 31, 2013 and June 30, 2013, respectively. The decreases in cost per ad engagement over these periods were primarily due to an increase in supply of advertising inventory available in
our auctions, which was partially offset by increased demand for our Promoted Products. Supply of advertising inventory increased as we expanded the distribution of our Promoted Products to our mobile applications and additional markets outside of
the United States in 2012. The increase in advertising inventory provided us with additional opportunities to place ads on our platform. This increase in advertising inventory combined with efforts in the three months ended June 30, 2013 to improve
the advertiser experience by refining our algorithms to balance the distribution of an advertisers budget throughout the day reduced the amount that advertisers were required to bid to win auctions for our pay-for-performance Promoted
Products. This reduction in cost per ad engagement made our Promoted Products more attractive for our existing advertisers and new advertisers, including small and medium sized businesses with smaller advertising budgets, as well as international
advertisers. As we continue to optimize for advertiser value and the overall user experience, the cost per ad engagement may continue to decline over time, and we expect the cost per ad engagement to decline in the near term. In the event that cost
per ad engagement continues to decline, and we are unable to continue to offset the impact of such decreases on advertising revenue by increasing the number of ad engagements, our advertising revenue would decline. We believe that, in order to
increase the cost per ad engagement, we will need to increase advertiser demand for our Promoted Products by enhancing the value of such products. We plan to increase the value of our Promoted Products by increasing the size and engagement of our
user base, improving our ability to target advertising to our users interests and improving the ability of our advertisers to optimize their campaigns and measure the results of their campaigns. We also believe our goal of maximizing the
long-term value of our platform for our users and advertisers should make Promoted Products more attractive to our existing and new advertisers and allow us to deliver more relevant ads on our platform.

In addition, our advertising revenue per timeline view in the United States is substantially higher than our advertising revenue per
timeline view in the rest of the world. For example, during the three months ended June 30, 2013, our advertising revenue per timeline view in the United States was $2.17 and our advertising revenue per timeline view in the rest of the world was
$0.30. We expect this disparity to continue for the foreseeable future. Accordingly, to the extent the number of international users and engagement by international users grow faster than U.S. users and engagement by U.S. users, total advertising
revenue per timeline view may be adversely impacted even if total advertising revenue continues to increase.

We have
also been able to generate significant revenue through our mobile applications. We introduced Promoted Products on our iOS and Android mobile applications in February 2012, and have since expanded to include Promoted Products on our other mobile
applications. In the three months ended June 30, 2013, over 65% of our advertising revenue was generated from mobile devices. We have experienced strong growth in advertising revenue from mobile devices because user engagement, as measured by
timeline views, is significantly higher on mobile applications than on our desktop applications, and we expect this trend to continue. However, Promoted Accounts and Promoted Trends receive less prominence on our mobile applications than they
do on our desktop applications, which means that fewer users see them displayed on our mobile applications, resulting in fewer ad engagements with Promoted Accounts and fewer impressions of Promoted

Trends on mobile applications. Primarily as a result of Promoted Accounts and Promoted Trends receiving less prominence on mobile applications, we have generated higher advertising revenue per
timeline view on our desktop applications than on our mobile applications. Although advertising revenue per timeline view on our desktop applications is higher than advertising revenue per timeline view on our mobile applications, the substantial
majority of our timeline views and advertising revenue is generated from mobile applications. Accordingly, to the extent that user engagement on mobile applications continues to increase faster than user engagement on our desktop applications,
advertising revenue per timeline view may be adversely impacted even if total advertising revenue continues to increase.

We intend to continue to increase the monetization of our platform by improving the targeting capabilities of our advertising
services to enhance the value of our Promoted Products for advertisers, expanding our sales efforts to reach advertisers in additional international markets, opening our platform to additional advertisers through our self-serve advertising platform
and developing new ad formats for advertisers.

Effectiveness of Our Advertising Services. Advertisers can
use Twitter to communicate directly with their followers for free, but many choose to purchase our advertising services to reach a broader audience and further promote their brands, products and services. We believe that increasing the effectiveness
of our Promoted Products for advertisers will increase the amount that advertisers spend with us. We aim to increase the value of our Promoted Products by increasing the size and engagement of our user base, improving our ability to target
advertising to our users interests and improving the ability of our advertisers to optimize their campaigns and measure the results of their campaigns. We may also develop new advertising products and services.

International Expansion. We intend to invest in our international operations in order to expand our user base and
advertiser base and increase user engagement and monetization internationally. In the three months ended June 30, 2013, we had 169.1 million average MAUs internationally compared to 49.2 million average MAUs in the United States. In addition, our
number of users is growing at a faster rate in many international markets, such as Argentina, France, Japan, Russia, Saudi Arabia and South Africa. However, we derive the substantial majority of our advertising revenue from advertisers in the United
States. We also generate significantly more advertising revenue per timeline view in the United States than internationally, with advertising revenue per timeline view in the three months ended June 30, 2013 of $2.17 in the United States and $0.30
internationally. Further, because we record advertising revenue based on the billing location of our advertisers, engagement by international users with ads placed by advertisers located in the United States increases our advertising revenue per
timeline view in the United States. In order to increase our international advertising revenue, we plan to invest in our international operations. In the near term, we plan to increase the size of our sales and marketing support teams in Australia,
Brazil, Ireland and the Netherlands, and we plan to extend our self-serve advertising platform to countries outside of the United States.

We face challenges in increasing our advertising revenue internationally, including local competition, differences in advertiser demand,
differences in the digital advertising market and conventions, and differences in the manner in which Twitter is accessed and used internationally. We face competition from well established competitors in certain international markets, including
Kakao in South Korea and LINE in Japan. In addition, certain international markets are not as familiar with digital advertising in general, or with new forms of digital advertising, such as our Promoted Products. In these jurisdictions we are
investing to educate advertisers about the benefits of our advertising services. However, we expect that it may require a significant investment of time and resources to educate advertisers in many international markets. We also face challenges in
providing certain advertising products, features or analytics in certain international markets, such as the European Union, due to government regulation. In addition, in certain emerging markets, many users access

Twitter through feature phones with limited functionality, rather than through smartphones, our website or desktop applications. This limits our ability to deliver certain features to these users
and may limit the ability of advertisers to deliver compelling ads to users in these markets. We are investing to improve our applications for feature phones in order to improve our ability to monetize our products and services in international
markets.

Competition. We face significant competition for users and advertisers. We compete against many
companies to attract and engage users and for advertiser spend, including companies with greater financial resources and substantially larger user bases, such as Facebook (including Instagram), Google, LinkedIn, Microsoft and Yahoo!, which offer a
variety of Internet and mobile device-based products, services and content. In recent years there have been significant acquisitions and consolidation by and among our actual and potential competitors. We must compete effectively for users and
advertisers in order to grow our business and increase our revenue. We believe that our ability to compete effectively for users depends upon a number of factors, including the quality of our products and services; and our ability to compete
effectively for advertisers depends upon a number of factors, including our ability to offer attractive advertising products with unique targeting capabilities and the size of our active user base. We intend to continue to invest in research and
development to improve our products and services for users and advertisers and to grow our active user base in order to address the competitive challenges in our industry. As part of our strategy to improve our products and services, we may acquire
other companies to add engineering talent or complementary products and technologies.

Investment in
Infrastructure. We intend to increase the capacity and enhance the capability and reliability of our infrastructure. Our infrastructure is critical to providing users, platform partners, advertisers and data partners
access to our platform, particularly during major planned and unplanned events, such as elections, sporting events or natural disasters, when activity on our platform increases dramatically. As our user base and the activity on our platform grow, we
expect that investments and expenses associated with our infrastructure will continue to grow. These investments and expenses include the expansion of our data center operations and related operating costs, additional servers and networking
equipment to increase the capacity of our infrastructure and increased bandwidth costs.

Products and Services
Innovation. Our ability to increase the size and engagement of our user base, attract advertisers and increase our revenue will depend, in part, on our ability to improve existing products and services and to successfully
develop or acquire new products and services. We plan to continue to make significant investments in research and development and, from time to time, we may acquire companies to enhance our products, services and technical capabilities.

Investment in Talent. We intend to invest in hiring and retaining talented employees to grow our business and
increase our revenue. As of June 30, 2013, we had approximately 2,000 full-time employees, an increase of over 900 full-time employees, or approximately 90%, from June 30, 2012. We expect to grow headcount for the foreseeable future as we continue
to invest in our business. We have also made and intend to continue to make acquisitions that add engineers, designers, product managers and other personnel with specific technology expertise. In addition, we must retain our high-performing
personnel in order to continue to develop, sell and market our products and services and manage our business.

Seasonality. Advertising spending is traditionally strongest in the fourth quarter of each year. Historically, this
seasonality in advertising spending has affected our quarterly results, with higher sequential advertising revenue growth from the third quarter to the fourth quarter compared to sequential advertising revenue growth from the fourth quarter to the
subsequent first quarter. For example, our advertising revenue increased 63% and 45% between the third and fourth quarters of 2011 and 2012, respectively, while advertising revenue for the first quarter of 2012 and 2013 increased 37% and 1% compared
to the fourth quarter of 2011 and 2012, respectively. In addition, advertising

revenue per timeline view increased 31% between the third and fourth quarter of 2012, while advertising revenue per timeline view decreased 13% between the fourth quarter of 2012 and the first
quarter of 2013. The rapid growth in our business may have partially masked seasonality to date and the seasonal impacts may be more pronounced in the future.

Stock-Based Compensation Expense. Since May 2011, we have been granting RSUs to our employees. The Pre-2013 RSUs vest upon the satisfaction of both a service condition and a
performance condition. The service condition for a majority of the Pre-2013 RSUs is satisfied over a period of four years. The performance condition will be satisfied on the earlier of (i) the date that is the earlier of (x) six months
after the effective date of this offering or (y) March 8th of the calendar year following the effective date of this offering (which we may elect to accelerate to February 15th); and (ii) the date of a change in control. As of June
30, 2013, no stock-based compensation expense had been recognized for the Pre-2013 RSUs because a qualifying event as described above was not probable. In the quarter in which this offering is completed, we will begin recording stock-based
compensation expense based on the grant-date fair value of the Pre-2013 RSUs using the accelerated attribution method, net of estimated forfeitures. If this offering had been completed on June 30, 2013, we would have recorded $329.6 million of
cumulative stock-based compensation expense related to the Pre-2013 RSUs on that date, and an additional $234.2 million of unrecognized stock-based compensation expense related to the Pre-2013 RSUs, net of estimated forfeitures, would be
recognized over a weighted-average period of approximately three years. In addition to stock-based compensation expense associated with the Pre-2013 RSUs, as of June 30, 2013, we had unrecognized stock-based compensation expense of approximately
$296.7 million related to other outstanding equity awards, after giving effect to estimated forfeitures, which we expect to recognize over a weighted-average period of approximately four years. Further, we made grants of equity awards after
June 30, 2013, and we have unrecognized stock-based compensation expense of $452.9 million related to such equity awards, after giving effect to estimated forfeitures, which we expect to recognize over a weighted-average period of approximately
four years.

On the settlement dates for the Pre-2013 RSUs, we may choose to allow our employees who are not executive officers to sell
shares of our common stock received upon the vesting and settlement of the Pre-2013 RSUs in the public market to satisfy their income tax obligations related to the vesting and settlement of such awards, or we may choose to undertake a net
settlement of these awards and withhold and remit income taxes on behalf of the holders of Pre-2013 RSUs at the applicable minimum statutory rates. We expect the applicable minimum statutory rates to be approximately 40% on average, and the income
taxes due would be based on the then-current value of the underlying shares of our common stock. Based on the number of Pre-2013 RSUs outstanding as of June 30, 2013 for which the service condition had been satisfied on that date, and assuming
(i) the performance condition had been satisfied on that date and (ii) that the price of our common stock at the time of settlement was equal to $ , which is the midpoint of the estimated
offering price range set forth on the cover page of this prospectus, we estimate that this tax obligation on the initial settlement date would be approximately $ in the aggregate. The amount of this
obligation could be higher or lower, depending on the price of shares of our common stock on the initial settlement date for the Pre-2013 RSUs. To settle these Pre-2013 RSUs on the initial settlement date, assuming a 40% tax withholding rate, if we
choose to undertake a net settlement of all of these awards rather than allowing our employees who are not executive officers to sell shares of our common stock in the public market to satisfy their income tax obligations related to the vesting and
settlement of such awards, we would expect to deliver an aggregate of approximately shares of our common stock to Pre-2013 RSU holders and withhold an aggregate of approximately
shares of our common stock. In connection with these net settlements, we would withhold and remit the tax liabilities on behalf of the Pre-2013 RSU holders to the relevant tax
authorities in cash.

Promoted Tweets. Promoted Tweets, which are labeled as promoted, appear within a users timeline or search results
just like an ordinary Tweet regardless of device, whether it be desktop or mobile. Using our proprietary algorithms and understanding of the interests of each user, we can deliver Promoted Tweets that are intended to be relevant to a particular
user. We enable our advertisers to target an audience based on our users Interest Graphs. Our Promoted Tweets are pay-for-performance advertising that are priced through an auction. We recognize advertising revenue when a user engages with a
Promoted Tweet.



Promoted Accounts. Promoted Accounts, which are labeled as promoted, appear in the same format and place as accounts
suggested by our Who to Follow recommendation engine. Promoted Accounts provide a way for our advertisers to grow a community of users who are interested in their business, products or services. Our Promoted Accounts are pay-for-performance
advertising that are priced through an auction. We recognize advertising revenue when a user follows a Promoted Account.



Promoted Trends. Promoted Trends, which are labeled as promoted, appear at the top of the list of trending topics for
an entire day in a particular country or on a global basis. When a user clicks on a Promoted Trend, search results for that trend are shown in a timeline and a Promoted Tweet created by the advertiser is displayed to the user at the top of those
search results. We sell our Promoted Trends on a fixed-fee-per-day basis. We feature one Promoted Trend per day per geography, and recognize advertising revenue from a Promoted Trend when it is displayed on our platform.

Data Licensing

We offer data licenses that allow our data partners to access, search and analyze historical and real-time data on our platform, which data consists of public Tweets and their content. Our data partners generally
purchase licenses to access all or a portion of our data for a fixed period, which is typically two years. We recognize data licensing revenue as the licensed data is made available to our data partners. In the six months ended June 30, 2013, our
top five data partners accounted for approximately 75% of our data licensing revenue, and approximately 10% of total revenue in the period. We expect data licensing revenue to decrease as a percentage of our total revenue over time.

Cost of Revenue and Operating Expenses

Cost of Revenue

Cost of
revenue consists primarily of data center costs related to our co-located facilities, which include lease and hosting costs, related support and maintenance costs and energy and bandwidth costs, as well as depreciation of our servers and networking
equipment, and personnel-related costs, including salaries, benefits and stock-based compensation, for our operations teams. Cost of revenue also includes allocated facilities and other supporting overhead costs, amortization of acquired intangible
assets and capitalized labor costs. Many of the elements of our cost of revenue are relatively fixed, and cannot be reduced in the near term to offset any decline in our revenue.

We plan to continue increasing the capacity and enhancing the capability and reliability of our
infrastructure to support user growth and increased activity on our platform. We anticipate a significant increase in cost of revenue in the year ending December 31, 2013 as a result of the stock-based compensation expense associated with the
Pre-2013 RSUs as described in Factors Affecting Our Future PerformanceStock-Based Compensation Expense. We expect that cost of revenue will increase in dollar amount for the foreseeable future and vary in the near term from
period to period as a percentage of revenue.

Research and Development

Research and development expenses consist primarily of personnel-related costs, including salaries, benefits and stock-based compensation, for our
engineers and other employees engaged in the research and development of our products and services. In addition, research and development expenses include allocated facilities and other supporting overhead costs.

We plan to continue to hire employees for our engineering, product management and design teams to support our research and development efforts. We
anticipate a significant increase in research and development expenses in the year ending December 31, 2013 as a result of the stock-based compensation expense associated with the Pre-2013 RSUs as described in Factors Affecting Our
Future PerformanceStock-Based Compensation Expense. We expect that research and development costs will increase in dollar amount for the foreseeable future and vary in the near term from period to period as a percentage of revenue.

Sales and Marketing

Sales and marketing expenses consist primarily of personnel-related costs, including salaries, benefits and stock-based compensation for our employees engaged in sales, sales support, commissions, business
development and media, marketing, corporate communications and customer service functions. In addition, marketing and sales-related expenses also include market research, tradeshows, branding, marketing and public relations costs, as well as
allocated facilities and other supporting overhead costs.

We plan to continue to invest in sales and marketing to expand
internationally, grow our advertiser base and increase our brand awareness. We anticipate a significant increase in sales and marketing expenses in the year ending December 31, 2013 as a result of the stock-based compensation expense associated
with the Pre-2013 RSUs as described in Factors Affecting Our Future PerformanceStock-Based Compensation Expense. We expect that sales and marketing expenses will increase in dollar amount for the foreseeable future and vary
in the near term from period to period as a percentage of revenue.

General and Administrative

General and administrative expenses consist primarily of personnel-related costs, including salaries, benefits and stock-based compensation, for our
executive, finance, legal, information technology, human resources and other administrative employees. In addition, general and administrative expenses include fees and costs for professional services, including consulting, third-party legal and
accounting services and facilities and other supporting overhead costs that are not allocated to other departments.

We plan to continue
to expand our business both domestically and internationally, and expect to increase the size of our general and administrative function to help grow our business. We expect that we will incur additional general and administrative expenses as a
result of being a publicly-traded company.

We also anticipate a significant increase in general and administrative expenses in the year ending December 31, 2013 as a result of the stock-based compensation expense associated with the
Pre-2013 RSUs as described in Factors Affecting Our Future PerformanceStock-Based Compensation Expense. We expect that general and administrative expenses will increase in dollar amount for the foreseeable future and vary in
the near term from period to period as a percentage of revenue.

Provision (Benefit) for Income Taxes

Provision for income taxes consists of federal and state income taxes in the United States and income taxes in certain foreign jurisdictions, and
deferred income taxes and changes in related valuation allowance reflecting the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax
purposes.

As of December 31, 2012, we had $298.8 million of federal and $216.7 million of state net operating loss
carryforwards available to reduce future taxable income. These net operating loss carryforwards will begin to expire for federal income tax purposes and state income tax purposes in 2027 and 2017, respectively. We expect our net operating loss
carryforwards to increase in the quarter in which we initially settle a portion of the Pre-2013 RSUs as a result of the vesting of such RSUs. We also have research credit carryforwards of $6.6 million and $10.5 million for federal and
state income tax purposes, respectively. The federal research credit carryforward will begin to expire in 2027. The state research credit carryforward has no expiration date. Utilization of the net operating loss carryforwards and research
carryforwards credit may be subject to an annual limitation due to the ownership change limitations set forth in the Code, and similar state provisions. Any annual limitation may result in the expiration of net operating losses and research credits
before utilization.

Results of Operations

The following tables set forth our consolidated statement of operations data for each of the periods presented:

Year Ended December 31,

Six Months EndedJune 30,

2010

2011

2012

2012

2013

(In thousands)

(Unaudited)

Revenue

Advertising services

$

7,321

$

77,710

$

269,421

$

101,302

$

221,432

Data licensing

20,957

28,603

47,512

21,057

32,203

Total revenue

$

28,278

$

106,313

$

316,933

$

122,359

$

253,635

Costs and
expenses(1)

Cost of revenue

43,168

61,803

128,768

58,157

91,828

Research and development

29,348

80,176

119,004

46,345

111,837

Sales and marketing

6,289

25,988

86,551

34,105

77,697

General and administrative

16,952

65,757

59,693

30,758

35,096

Total costs and expenses

95,757

233,724

394,016

169,365

316,458

Loss from operations

(67,479

)

(127,411

)

(77,083

)

(47,006

)

(62,823

)

Interest income (expense), net

55

(805

)

(2,486

)

(890

)

(2,746

)

Other income (expense), net

(117

)

(1,530

)

399

(12

)

(2,548

)

Loss before income taxes

(67,541

)

(129,746

)

(79,170

)

(47,908

)

(68,117

)

Provision (benefit) for income taxes

(217

)

(1,444

)

229

1,196

1,134

Net loss

$

(67,324

)

$

(128,302

)

$

(79,399

)

$

(49,104

)

$

(69,251

)

(1)

Costs and expenses include stock-based compensation expense as follows:

The following table sets forth our consolidated statement of operations data for each of the periods
presented as a percentage of revenue:

Year EndedDecember 31,

Six MonthsEndedJune 30,

2010

2011

2012

2012

2013

Revenue

Advertising services

26

%

73

%

85

%

83

%

87

%

Data licensing

74

27

15

17

13

Total Revenue

100

100

100

100

100

Costs and expenses

Cost of revenue

153

58

41

48

36

Research and development

104

75

38

38

44

Sales and marketing

22

24

27

28

31

General and administrative

60

62

19

25

14

Total costs and expenses

339

220

124

138

125

Loss from operations

(239

)

(120

)

(24

)

(38

)

(25

)

Interest income (expense), net



(1

)

(1

)

(1

)

(1

)

Other income (expense), net



(1

)





(1

)

Loss before income taxes

(239

)

(122

)

(25

)

(39

)

(27

)

Provision (benefit) for income taxes

(1

)

(1

)



1



Net loss

(238

)%

(121

)%

(25

)%

(40

)%

(27

)%

Six Months Ended June 30, 2012 and 2013

Revenue

Six Months EndedJune 30,

2012

2013

% Change

(Unaudited, in thousands)

Advertising services

$

101,302

$

221,432

119

%

Data licensing

21,057

32,203

53

%

Total revenue

$

122,359

$

253,635

107

%

Revenue in the six months ended June 30, 2013 increased by $131.3 million compared to the six months ended
June 30, 2012.

In the six months ended June 30, 2013, advertising revenue increased by 119% compared to the six months ended June 30,
2012. The increase was primarily attributable to a 79% increase in timeline views in the six months ended June 30, 2013, compared to the same period in the prior year, as well

as an increase in demand from advertisers that drove an increase in advertising revenue per timeline view of 22% in the six months ended June 30, 2013 compared to the same period in the prior
year. The increase in timeline views was driven by a 44% increase in average MAUs, and a 24% increase in the user engagement levels of MAUs, as measured by timeline views per MAU, in the six months ended June 30, 2013 compared to the same period in
the prior year. The increase in advertising revenue per timeline view was primarily driven by a 199% increase in ad engagements per timeline view, partially offset by a 59% decrease in average cost per ad engagement in the six months ended June 30,
2013 compared to the same period in the prior year. The increase in ad engagements per timeline view, combined with the increase in timeline views, resulted in a 435% increase in the number of ad engagements in the six months ended June 30, 2013
compared to the same period in the prior year. Advertising revenue also benefited from sales of our Promoted Products on our mobile applications, which were launched in the six months ended June 30, 2012, as well as from an increase in international
revenue.

In the six months ended June 30, 2013, data licensing revenue increased by 53% compared to the six months ended June 30, 2012.
The increase in data licensing revenue was attributable to a 25% net increase in licensing fees from existing data partners, as well as an increase in licensing fees from new data partners in the six months ended June 30, 2013 compared to the same
period in the prior year.

Cost of Revenue

Six Months EndedJune 30,

2012

2013

% Change

(Unaudited, dollar amountsin thousands)

Cost of revenue

$

58,157

$

91,828

58

%

Cost of revenue as a percentage of revenue

48

%

36

%

In the six months ended June 30, 2013, cost of revenue increased by $33.7 million compared to the six months
ended June 30, 2012. The increase was primarily attributable to a $14.4 million increase in depreciation expense related to capital leases for additional server and networking equipment, a $7.7 million increase in allocated facilities and
other supporting overhead costs, a $6.4 million increase in personnel-related costs, mainly driven by an increase in average employee headcount and recognition of stock-based compensation expense related to Post-2013 RSUs we began to grant in
February 2013, and a $5.2 million increase in data center costs related to our co-located facilities.

Research and Development

Six Months EndedJune 30,

2012

2013

% Change

(Unaudited, dollar amountsin thousands)

Research and development

$

46,345

$

111,837

141

%

Research and development as a percentage of revenue

38

%

44

%

In the six months ended June 30, 2013, research and development expense increased by $65.5 million compared to
the six months ended June 30, 2012. The increase was primarily attributable to a $61.5 million increase in personnel-related costs, mainly driven by an increase in average employee headcount and recognition of stock-based compensation expense
related to Post-2013 RSUs we began to grant in February 2013, and a $13.1 million increase in allocated facilities and other supporting overhead costs. These increases were partially offset by a $9.1 million increase in the capitalization
of costs associated with developing software for internal use.

In the six months ended June 30, 2013, sales and marketing expenses increased by $43.6 million compared to the
six months ended June 30, 2012. The increase was primarily attributable to a $26.6 million increase in personnel-related costs, mainly driven by an increase in average employee headcount and recognition of stock-based compensation expense
related to RSUs granted to domestic employees and other service providers starting in February 2013, or Post-2013 RSUs, an $11.2 million increase in marketing and sales-related expenses and a $5.8 million increase in allocated facilities
and other supporting overhead costs.

General and Administrative

Six Months EndedJune 30,

2012

2013

% Change

(Unaudited, dollar amountsin thousands)

General and administrative

$

30,758

$

35,096

14

%

General and administrative as a percentage of revenue

25

%

14

%

In the six months ended June 30, 2013, general and administrative expenses increased by $4.3 million compared
to the six months ended June 30, 2012. The increase was primarily attributable to an increase in costs for professional services of $6.9 million and a $4.3 million increase in personnel-related costs, mainly driven by an increase in
average employee headcount. These increases were partially offset by a $6.9 million decrease in unallocated facilities and other supporting overhead costs, resulting from increased allocation of overhead costs to other functions with higher
headcount growth.

Provision (Benefit) for Income Taxes

Six Months EndedJune 30,

2012

2013

(Unaudited,

in thousands)

Provision for income taxes

$

1,196

$

1,134

Our provision for income taxes in the six months ended June 30, 2013 did not change significantly compared to the
six months ended June 30, 2012, resulting in income tax expense of $1.1 million in the six months ended June 30, 2013. The slight decrease was primarily due to a reduction in state income taxes and tax benefits arising from acquisitions, offset by
an increase in foreign tax expense.

2012 Compared to 2011. Revenue in 2012 increased by $210.6 million
compared to 2011.

In 2012, advertising revenue increased by 247% compared to 2011. The increase was primarily attributable to the
expansion of our advertising service offerings in the second half of 2011 and the first half of 2012, as well as a 59% increase in average MAUs in 2012 compared to 2011. We expanded our advertising service offerings through the introduction of
Promoted Tweets in all user timelines in October 2011 and Promoted Products on mobile applications in February 2012.

In 2012, data
licensing revenue increased by 66% compared to 2011. The increase in data licensing revenue was primarily attributable to a 51% net increase in licensing fees from existing data partners in 2012 compared to 2011, and to a lesser extent from an
increase in licensing fees from new data partners.

2011 Compared to 2010. Revenue in 2011 increased by
$78.0 million compared to 2010.

In 2011, advertising revenue increased by 961% compared to 2010. The increase was primarily
attributable to the full year impact of Promoted Products in 2011, as these products were introduced in 2010, an expansion in our advertising service offerings in 2011 and a 115% increase in average MAUs in 2011 compared to 2010. We introduced our
first Promoted Product, Promoted Trends, in June 2010 and expanded our advertising service offerings through the introduction of Promoted Tweets in all user timelines in October 2011.

In 2011, data licensing revenue increased by 36% compared to 2010. The increase in data licensing revenue was primarily attributable to a 22% net
increase in licensing fees from existing data partners in 2011 compared to 2010.

Cost of Revenue

Year Ended December 31,

2010 to 2011% Change

2011 to 2012% Change

2010

2011

2012

(In thousands)

Cost of revenue

$

43,168

$

61,803

$

128,768

43

%

108

%

Cost of revenue as a percentage of revenue

153

%

58

%

41

%

2012 Compared to 2011. In 2012, cost of revenue increased by $67.0 million
compared to 2011. The increase was primarily attributable to a $28.9 million increase in depreciation expense related to additional server and networking equipment capital leases, a $14.0 million increase in amortization of acquired intangible
assets, a $10.0 million increase in data center costs related to our co-located facilities, a $7.8 million increase in personnel-related costs, mainly driven by an increase in average employee headcount and a $6.3 million increase in
allocated facilities and other supporting overhead expenses.

2011 Compared to 2010. In 2011, cost of
revenue increased by $18.6 million compared to 2010. The increase was primarily attributable to a $17.4 million increase in depreciation expense related to additional server and networking equipment capital leases and an $8.0 million
increase in personnel-related costs (including a $1.1 million charge recorded in connection with the 2011 tender offer which is described below), mainly driven by an increase in average employee headcount. These increases were partially offset
by a $7.1 million decrease in data center costs as a result of our move from a third-party hosting solution to a co-located facility.

In 2011, the investors in our Series G convertible preferred stock financing commenced a tender offer to purchase shares of our common stock and Series A through Series F convertible preferred

stock from our employees, consultants and other stockholders. The tender offer closed in September 2011, and we recorded $34.7 million of stock-based compensation expense related to the
excess of the price per share of our common stock paid to our employees and consultants in the tender offer over the fair value of the tendered shares. This $34.7 million of stock-based compensation expense in 2011 was allocated among cost of
revenue, research and development expenses, sales and marketing expenses and general and administrative expenses in amounts of $1.1 million, $19.1 million, $0.4 million and $14.1 million, respectively.

Research and Development

Year Ended December 31,

2010 to 2011% Change

2011 to 2012% Change

2010

2011

2012

(Dollar amounts in thousands)

Research and development

$

29,348

$

80,176

$

119,004

173

%

48

%

Research and development as a percentage of revenue

104

%

75

%

38

%

2012 Compared to 2011. In 2012, research and development expenses increased by
$38.8 million compared to 2011. The increase was primarily attributable to a $21.7 million increase in personnel-related costs, mainly driven by an increase in average employee headcount, and a $23.9 million increase in allocated
facilities and other supporting overhead expenses. These increases were partially offset by a $6.8 million increase in the capitalization of costs associated with developing software for internal use.

2011 Compared to 2010. In 2011, research and development expenses increased by $50.8 million compared to 2010.
The increase was primarily attributable to a $56.7 million increase in personnel-related costs (including a $19.1 million charge recorded in connection with the 2011 tender offer), mainly driven by an increase in average employee
headcount. These increases were partially offset by a $3.8 million increase in the capitalization of costs associated with developing software for internal use and a $2.1 million decrease in amortization of acquired intangible assets.

Sales and Marketing

Year Ended December 31,

2010 to 2011% Change

2011 to 2012% Change

2010

2011

2012

(Dollar amounts in thousands)

Sales and marketing

$

6,289

$

25,988

$

86,551

313

%

233

%

Sales and marketing as a percentage of revenue

22

%

24

%

27

%

2012 Compared to 2011. In 2012, sales and marketing expenses increased by
$60.6 million compared to 2011. The increase was primarily attributable to a $34.6 million increase in personnel-related costs, mainly driven by an increase in average employee headcount, a $15.9 million increase in allocated
facilities and other supporting overhead expenses and a $10.1 million increase in marketing and sales-related expenses.

2011
Compared to 2010. In 2011, sales and marketing expenses increased by $19.7 million compared to 2010. The increase was primarily attributable to a $16.3 million increase in personnel-related costs, mainly driven
by an increase in average employee headcount, a $1.9 million increase in allocated facilities and other supporting overhead expenses and a $1.5 million increase in marketing and sales-related expenses.

2012 Compared to 2011. In 2012, general and administrative expense decreased by
$6.1 million compared to 2011. The decrease was primarily attributable to a $19.9 million decrease in unallocated facilities and supporting costs, driven by slower headcount growth in the general and administrative function relative to other
functional areas, partially offset by a $7.9 million increase in personnel-related costs (which takes into account a $14.1 million charge recorded in 2011 in connection with the 2011 tender offer), mainly driven by an increase in average employee
headcount and an increase of $5.9 million in fees and costs for professional services. Excluding the impact of the 2011 tender offer, personnel-related costs increased by $22.0 million in 2012 compared to 2011.

2011 Compared to 2010. In 2011, general and administrative expenses increased by $48.8 million compared to 2010.
The increase was primarily due to a $29.3 million increase in personnel-related costs (including a $14.1 million charge recorded in connection with the 2011 tender offer), which was driven by an increase in average employee headcount, a
$12.0 million increase in fees and costs for professional services and a $7.5 million increase in unallocated facilities and other supporting costs.

Provision (Benefit) for Income Taxes

Year Ended December 31,

2010

2011

2012

(In thousands)

Provision (benefit) for income taxes

$

(217)

$

(1,444)

$

229

2012 Compared to 2011. Our provision for income taxes in 2012 increased by
$1.7 million compared to an income tax benefit of $1.4 million in 2011. The increase was primarily due to the increased tax expenses in foreign and state jurisdictions, partially offset by the decrease in income tax benefit arising from
acquisitions.

2011 Compared to 2010. Our benefit for income taxes in 2011 increased by $1.2 million
compared to an income tax benefit of $0.2 million in 2010. The increase was primarily attributable to an increase in the income tax benefit arising from acquisitions.

The following table sets forth our unaudited consolidated statement of operations data for each of the ten quarters in the period ended June 30, 2013. The unaudited quarterly statement of operations data set forth
below have been prepared on a basis consistent with our audited annual consolidated financial statements and include, in our opinion, all normal recurring adjustments necessary for a fair statement of the financial information contained in those
statements. Our historical results are not necessarily indicative of the results that may be expected in the future. The following quarterly financial data should be read in conjunction with our audited consolidated financial statements and the
related notes included elsewhere in this prospectus.

Three Months Ended

Mar. 31,2011

Jun. 30,2011

Sep. 30,2011

Dec. 31,2011

Mar. 31,2012

Jun. 30,2012

Sep. 30,2012

Dec. 31,2012

Mar. 31,2013

Jun. 30,2013

(Unaudited, in thousands)

Consolidated Statement of Operations Data:

Revenue

Advertising revenue

11,561

13,619

19,942

32,588

44,500

56,802

68,665

99,454

100,460

120,972

Data licensing

6,349

7,154

6,482

8,618

9,813

11,244

13,662

12,793

13,883

18,320

Total revenue

$

17,910

$

20,773

$

26,424

$

41,206

$

54,313

$

68,046

$

82,327

$

112,247

$

114,343

$

139,292

Costs and expenses(1)

Cost of revenue

15,453

10,632

15,719

19,999

27,629

30,528

33,693

36,918

41,255

50,573

Research and development

10,163

14,687

34,721

20,605

18,976

27,369

32,319

40,340

47,574

64,263

Sales and marketing

3,652

5,147

7,368

9,821

14,450

19,655

23,662

28,784

32,439

45,258

General and administrative

8,709

13,244

27,776

16,028

13,389

17,369

13,954

14,981

16,982

18,114

Total costs and expenses

37,977

43,710

85,584

66,453

74,444

94,921

103,628

121,023

138,250

178,208

Loss from operations

(20,067

)

(22,937

)

(59,160

)

(25,247

)

(20,131

)

(26,875

)

(21,301

)

(8,776

)

(23,907

)

(38,916

)

Interest income (expense), net

(260

)

(188

)

(204

)

(153

)

(377

)

(513

)

(766

)

(830

)

(1,233

)

(1,513

)

Other income (expense), net

(17

)

(1,437

)

36

(112

)

(259

)

247

938

(527

)

(1,529

)

(1,019

)

Loss before income taxes

(20,344

)

(24,562

)

(59,328

)

(25,512

)

(20,767

)

(27,141

)

(21,129

)

(10,133

)

(26,669

)

(41,448

)

Provision (benefit) for income taxes





(1,993

)

549

754

442

461

(1,428

)

357

777

Net loss

$

(20,344

)

$

(24,562

)

$

(57,335

)

$

(26,061

)

$

(21,521

)

$

(27,583

)

$

(21,590

)

$

(8,705

)

$

(27,026

)

$

(42,225

)

Other Financial Information:

Adjusted EBITDA(2)

$

(14,411

)

$

(10,817

)

$

(13,145

)

$

(4,462

)

$

(875

)

$

1,545

$

2,923

$

17,571

$

11,745

$

9,647

Non-GAAP net loss(3)

$

(17,670

)

$

(16,088

)

$

(18,520

)

$

(13,255

)

$

(11,369

)

$

(10,863

)

$

(12,688

)

$

(271

)

$

(10,524

)

$

(16,364

)

(1)

Costs and expenses include stock-based compensation expense as follows: